chapter 6 hydrological consequences of climate variability and … · 2014. 5. 11. · chapter 6...

CHAPTER 6

Hydrological consequences of climate variability and impact on sustainability of the two great basins in the northwest of Mexico

M. Rangel-Medina1 & J.A. López-Ibarra2

1Universidad de Sonora, México; IDEAS S.C, México.2Comisión Nacional del Agua, Organismo de Cuenca Noroeste, México.

Abstract

The results of climate variability obtained using climatologically oriented analy-sis and hydro-meteorological statistics of north western Mexico are presented. This information has problems of temporal continuity and without a proper spatial distribution of stations, mainly because they focus on lowland of the basins of the study areas of Sonora and Yaqui rivers. Those data were adjusted to solve all of this confl ict. The objective was to analyse the variability of recent years in the Hydrological Region 09, Sonora South, which has been affected by a decrease in rainfall and scarcity of runoff, affecting water availability in the dams, which is an important factor of the regional economy. Moreover, the occurrence of tropical cyclones has increased in the last decade producing extreme events as occasional heavy rains in coastal regions, generating heavy fl oods. This chapter determines the variability in the inland rivers. Drought is analysed as a part of climate variability using the rainfall and solving with a dimensionless index called the Standardized Precipitation Index (SPI), as a criterion to differentiate when we must consider that the region is in a drought unlike its permanent condition of arid and semi-arid dryness. The analysis solves estimates of climate variability in north western Mexico and defi nes with certainty the risk of the population to extreme events. The authors provide recommendations for managing the elements that support the sustainability of the population. The results were compared with the behaviour of runoff and historical rainfall in the two main basins. It is concluded that, although both basins are located in the same hydrological region, Sonora and Yaqui rivers have different conditions of climate variability.Keywords: Climate variability, hydrological impacts, watershed sustainability.

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88 Ecological Dimensions for Sustainable Socio Economic Development

1 Introduction

Since the beginning of geological time, a permanent feature of climate variability has been man’s constant presence, always determined essentially by natural vari-ables (change in the Earth’s rotation axis, volcanic eruptions, solar variations, land-forms, continental distribution, etc.) and now it is presumed that the action of man is a negligible induction in climate variability and change, so this issue is a strate-gic one widely discussed in scientifi c, political and social circles and has a direct impact on models of economic development of countries, in particular the grow-ing industrialization, which has weakened its sustainability. However, the climate variability pushes the debate into the extreme events: excess or scarcity of water. Therefore, it is very common in many countries that the authorities are ready every year to help the population after the tropical cyclones or the discussion among farmers and governments asking for considering the existence of a drought to help with subventions. The meaning of drought is that of a natural phenomenon that occurs when rainfall and water availability in a period of time and in a given region is less than the historical average registered and when this gap is large enough and long enough to damage human activities. The latter point becomes relevant since it acts against the economy of societies. However, the discussion is more sensitive in semi-arid and arid regions where water scarcity is a permanent condition, that is, under these conditions the equilibrium can be broken easily and even though it sounds impossible, mankind must balance their needs with the availability and adjust their production activities and their settlements with the climate variability.

In the case study, the hydrologic conditions in the north-western region of Mexico, climate variability was expressed in the rivers, after 12 years of meteoro-logical drought (1995–2007), with a decline in supply from surface runoff, falling to a point where the storage of dams was an average of 10% in 2004, and which led to a storage never seen before of 320 hm3 in the Yaqui river, because the worst year was 1953, with 639 hm3, double that of 2004. This serious crisis in agricultural drought was countered by groundwater; however, the valley left their sustainability, losing three consecutive crops (2002–2004) and it stopped electricity generation. For its part, the Sonora River ends at the Abelardo L. Rodriguez dam (ARD), located in Hermosillo the capital of the state of Sonora. This dam was declared zero storage since December 1998 and still goes on [1]. The Sonora River basin accounts for approximately 34% of the gross income domestic product of the state of Sonora; thus, the water shortage has also been substituted only with ground water, so their aquifers have severe imbalances induced by over-pumping [2].

1.1 Hydrology and water management in the region

The state of Sonora is one of 31 states of Mexico; it is located in the northwest of the republic and has a surface of 182,052 km2, which means 9.2% of the country, ranking second nationally in size. Its capital is Hermosillo, located in the central portion of the state, Fig. 1. The population of the state is approxi-mately 2.4 million inhabitants [3]. The basins of the country are organized into


Hydrological Consequences of Climate Variability and Impact 89

37 hydrological regions. The basins of Sonora and Yaqui rivers are located in the hydrological region 9, Sonora South [4], Fig. 1. This region is located between 27° and 31° 20' north latitude and 107° and 112° 15' west longitude. It has a surface of 136,518 km2 of which 3787 km2 correspond to the United States of America [5]. The most important currents are rivers Sonora, Yaqui and Mayo, all of whose draining comes from the Sierra Madre Occidental, from the north and northeast to west, in direction to the Gulf of California.

About the natural condition of this region and, considering the rates of precipi-tation, we can say that in Sonora, dynamic water balance is extremely fragile; therefore, an intensive extraction can easily exceed the volume of recharge of the water in the hydrologic annual cycle, understood this as that which develops on a seasonal basis and whose fl uctuations can be cyclical and multi-year basis in the man scale. The annual water balance, equivalent to this short cycle in the state, shows a high sensitivity to changes and sudden changes, which encourages the submission of annual cycles of drought and fl oods alternately, due to the alteration of various meteorological phenomena. It shows generation periods of rainfall extremes, low and high, consequently the runoff volumes can also vary considerably.

For example, Montgomery [6] calculated an annual average volume of precipi-tation of 97.8 km3 and a coeffi cient of 2.8% for the Sonora river basin, which generates a runoff of the order of 27.3 km3. Meanwhile, based on the statistics of the Sonora River gauging stations for the period 1960–1997, this study yielded a

Figure 1: Location of the study areas in the north-western region of Mexico.



mean runoff of 16.74 km3. This variation is considered representative of the cli-matic varying conditions of a semi-desert water cycle and includes part of a wet period (1984–1995) and a dry one (1996–2008).

2 The hydrological analysis

2.1 Hydrography of the study area

2.1.1 Sonora riverThe Sonora River basin has a hilly topography, except in the lower basin. The upper basin is rich in mineral deposits and the main copper mine is located near the origins of the current, in Cananea, Sonora. The watershed of this river has an area of 28.885 km2; it occupies around 16.7% of the north-western region and the Yaqui River basin occupies 38.5% [2]. The rest is occupied by fi ve other basins. Sonora River basin has two storage dams and fl ood control: Rodolfo Felix Valdez (EMD) and Abelardo L. Rodriguez (ARD) and practically ends downstream of the ARD, because it lost virtually its channel at this point and the coastal plain is now occupied by Hermosillo and in fl at areas up to their former Tastiota estuary mouth in the Gulf of California exist 40,000 ha of the Irrigation District 051, which operates pumping groundwater only. Along the Sonora River upstream of the ARD the uses are mainly for irriga-tion of the alluvial margins in the two main streams: rivers Sonora and San Miguel with small irrigation works. In the valley of the River El Zanjon, a tributary of San Miguel, superfi cial irrigation of different crops and an intensive use of groundwater for irrigation of around 30,000 ha of vineyards since the 1980s exist.

2.1.2 Yaqui riverThis basin is the largest and most important in the northwest; it generates signifi -cant volumes of runoff that is stored in three major dams which together have a storage capacity of 7200 hm3 for urban and industrial use, and irrigate 250,000 ha in two irrigation districts, and electricity generation. Characterized by a semi-arid climate, the Yaqui River basin comprises part of the Mexican states of Sonora and Chihuahua and a small portion of the state of Arizona in the United States. In the valley, modern agriculture is practiced and yields are high in the Irrigation Districts 041-Rio Yaqui and 018, probably the most important and modern irrigation area in Mexico. The Yaqui River drains an area of 69,590 km2 and an annual average runoff of 3600 hm3 up to the dam Alvaro Obregon which waters the valley with 270 km of canals in the district, approximately. The basin reaches an area of drain 72,590 km2 to its mouth in the Gulf of California, thus occupying 30% of the state territory [2].

2.2 Storage analysis of the dam systems

2.2.1 Sonora river

1. El Molinito Dam (EMD). The EMD is located on the Sonora River, about 15 km upstream of the ARD and 23 km from the city of Hermosillo. It was



inaugurated in 1991 with the purpose of controlling fl oods in the river, its stor-age capacity Maximum Water Level Ordinary (NAMO) was 150 hm3, however, a bathymetry of 2009, showed reduced storage capacity, with 130.2 hm3. Historically, the dam reached a maximum storage capacity of 169.8 hm3 in 1995 and for the fi rst time fell to 0.0 hm3 in April 2003 [2]. Since 1997 there has not been signifi cant recovery in volumes, which we see as correlation with the existence of the hydrological drought in this analysis.

2. Abelardo L. Rodríguez Dam (ARD). This dam is located east of the city of Hermosillo and downstream from the EMD. In 1948, its objective was to seize the Sonora River for irrigation and water supply. Their capacity of NAMO is 253.5 hm3. In 1992 it was put in a controlled discharge to achieve a capacity of 304.9 hm3 to NAMO. The current capacity is 284.5 to NAME hm3 to 228.4 m elevation while NAMO has a capacity of 219.5 hm3 for lift 226.98 m.a.s.l. [2]. Since 1998, the dam has been practically empty during several periods. Figure 2 shows the evolution of the volumes stored.

2.2.2 Yaqui riverThe Yaqui River is the largest river in the region. It is a controlled drainage in the Sonoran portion by the reservoir system Lazaro Cardenas (La Angostura), Plutarco Elias Calles (El Novillo) and General Alvaro Obregon (El Oviachic). This last site is considered the end of this stream, and up to where it occupies an area of 69,590 km2 and store 7200 hm3 [2].

Figure 2: Runoff (1942–2010) and storage (1952–2010) sonora and yaqui rivers.



1. Lazaro Cardenas Dam (LCD). This dam has been operating since 1942. It is located in the upper-middle portion of the basin. It has a capacity of 703.4 hm3 to NAMO, while at NAME is 1116.5 hm3. In October 2003, the dam had one of the lowest storages in its history with 69.3 hm3, less than 1967 and 1977, which were lower, with 32.2 hm3 and 17.5 hm3, respectively [2].

2. Plutarco Elías Calles Dam (PECD). Operating since 1964, it generates electric-ity and controls fl oods. It is situated some 151 km east of Hermosillo, in the middle basin of the Rio Yaqui. Their capacity to NAMO is 3020 hm3 and at NAME is 3628.6 hm3. In June 2003, it recorded one of the lowest storages in its history with 248.4 hm3, while in June 1999, the storage was 269.7 hm3 [2].

3. General Alvaro Obregon Dam (GAOD). It is located approximately 40 km north of Ciudad Obregon, in the municipality of Cajeme. Operating since 1952 for irrigation purposes in the district of the Yaqui River Valley, and for power generation and fl ood control. Its capacity is 3226.7 hm3 to NAMO, the NAME is 4200 hm3. In July 2003 it recorded storage of 308.6 hm3 which stands as a historic low [2], Fig. 2.

2.2.3 System-wide storage damsSince 1996, the volumes have been below the historical average, but the year 2003 still remains the lowest in the period. However, after reaching the minimum storage, the Yaqui River system renewed cycle with a signifi cant recovery; at the present it is about 7000 hm3 (December 2010).

2.3 Runoff analysis

2.3.1 Sonora river (gauging stations)

1. El Oregano-El Oregano II. Quantifi cation of the runoff of the Sonora River basin is made in the hydrometric station on the River II Oregano Sonora, upstream of the dam EMD, and El Cajon on the San Miguel de Horcasitas, near the town of same name. This station was installed in 1942 as the El Oregano and relocated upstream in 1998 as the El Oregano II, with the historical record of both stations average annual runoff of 105.5 hm3 for the period 1942–2009, Fig. 2. Their behaviour shows that from 1996 it is below its historical average and only in the year 2006 it was similar to the average annual runoff, but was not suffi cient to achieve signifi cant storage in the ARD [2].

2. Gauging station El Cajon. The hydrometric station El Cajon, installed in 1974, quantifi es the contributions of the San Miguel de Horcasitas River, the main tributary of Sonora on the right bank. The average annual runoff at this station is 34.2 hm3. Figure 2 shows the annual runoff of the gauging station for the period 1974–2009. The annual runoff for the year 1996 has been also below its historical average, with a slight upturn in 2000 and 2006 [2]. In both seasons this stream runoff have been minimal, suggesting the existence of a hydro-logical drought in the entire basin and is refl ected in the storage system of the Sonora River dams.



2.3.2 Yaqui riverFrom 1995 to 2003, the runoff in the watershed was scarce, a condition refl ected in the lower catchment of the reservoir system. Since 2003 the trend in the contribu-tions is on the rise. Runoff from the reservoir system of the Yaqui River show great variability with a mean value of 3494.6 hm3 for the period 1965–2009. Figure 2 shows that, since 1965, on 27 occasions (years) runoff were below this average value, 14 of them (52%) for the period 1994–2009. As the agricultural system of the Yaqui River valley depends almost entirely on the volume of water stored in dams and is of great importance for its operation and impact on economic activi-ties and social policies of the valley, so by falling into collapse the hydrological system by drought in the 2002–2003 cycle, the valley lost its sustainability of these activities and was adversely impacted.

3 Analysis of climatic variability

3.1 Variability as risk event and vulnerability

In our discussion we follow the defi nitions of event risk and outcome risk pre-sented by Sarewitz et al. [7]. and confi rmed by Pielke et al. [8]. ‘Event risk’ refers to the occurrence of a particular phenomenon, and in the context of hurricanes we focus on trends and projections of storm frequencies and intensities. ‘Vulnerability’ refers to ‘the inherent characteristics of a system that create the potential for harm’ but are independent from event risk. In the context of the economic impacts of tropical cyclones, vulnerability has been characterized in terms of trends in popu-lation and wealth that set the stage for storms to cause damage. ‘Outcome risk’ integrates considerations of vulnerability with event risk to characterize an event that causes losses. However to understand the variability it is necessary to analyse at fi rst the natural conditions and establish the background based on the statis-tics of every region. Therefore any kind of analysis of modern climate variability must consider two concepts established by the American Meteorological Society (1996) faced one against the other: atmospheric time versus climate. Atmospheric time includes the variations in short terms in the atmosphere (minutes to weeks). Climate is the variation media of the atmospheric time along a period of time (usually 30 years) [9].

3.2 Temperature analysis

Considering the previous criterion to analyse the variability of temperature and precipitation, we used a 70-year period (1938–2008), within which we found a number of cyclical variations of the typical climate in both basins. We can say cli-mates are dry, temperate and desert, xerophytic vegetation, forests and grasslands. The rains are erratic and occur in all seasons, even though some sites have regular and dry winter. The average annual temperature (AAT) is greater than 17.3°C, and below 26.1°C, depending on the area in which they are located. Figure 4 shows the



behaviour of the AAT for the stations located in the reservoirs of the basins of the Sonora and Yaqui, shown in Fig. 1.

The AAT in the Yaqui River have similar trend in the three large dams in the basin, Fig. 3A, 3B and 3C; its behaviour can be divided into three periods, and the fi rst was above the historical average, the second down, and the last above normal. In the LAD, Fig. 3A, since the late 1930s and until early 1960s, we observed that the AAT were above normal in the period from 1960 to 1990 temperatures are cool-est part of the historical record, but from the decade of the 1990s until the fi rst decade of this century, there are fl uctuations above the mean, and the climate was signifi cantly warmer. In PECD, Fig. 3B, central part of the Yaqui River basin, the AAT is similar to LCD, above normal in early 1960s and early 1970s, and from then until the mid-1990s temperatures were cooler. Finally, in the last period of the his-torical record, temperatures are above normal, except for the years 2007 and 2008.

In the Yaqui River as the topography descends from the upper parts of the Sierra Madre Occidental to the bottom of the basin, the temperatures rise and according to the weather station located at the GAOD, temperatures are the highest in the basin. In this dam the mean temperature record shows a period of warm tempera-tures from 1954 until 1964, and from 1965 until the early 1990s, the temperature was below the historical average. From 1994 and until the last period of the century, temperatures show a rising trend and are warmer than normal.

In the basin of the Sonora River, the behaviour of temperature trend was very different from the Yaqui River. At the meteorological station located in the city of Hermosillo, where dam ARD is located, Fig. 3D, average temperatures were below the historical average in 1960s and 1970s, and in the early 1980s the

Figure 3: Average annual temperature in the reservoirs of sonora and yaqui rivers.



temperatures were fl uctuating around the normal. However, from the 1990s there has been a marked temperature rise exceeding the historical average, if the behav-iour here is similar to the Yaqui River, with a warmer climate.

3.3 Pluvial precipitations analysis

The rainfall pattern in the Hydrological Region 9 is varied, but generally has two periods of occurrence, one between July and September when values are higher, and another that runs from December to February, when rainfall are considerably lower. In the basin of Sonora and Yaqui rivers the statistics of rainfall were anal-ysed, covering the period of 41 years (1968–2009). For the upper basin of Sonora, from its origins to ARD, the mean annual precipitation (MAP) is 399.9 mm, Fig. 4. The bar graph showed the annual behaviour of precipitation, with a maximum of 644.6 mm in 1984, while the lowest was recorded in 1998 with 228.1 mm; tak-ing the period 1995–2009, the MAP was 336.4 mm, which was below the annual average of 399.9 mm in the basin. According to the analysis, in this period the annual rainfall was the lowest in the historical record.

In the case of the Yaqui River basin, the MAP in the Yaqui River basin is 506.7 mm; the lower precipitation zone is located in the western portion, to the coastal plain, with 374.2 mm. In the east, rainfall is signifi cantly higher with Yecora station having MAP of 871 mm. Figure 4 shows that since 1995 except 1997, 2004 and 2007 rainfall in the basin had been below the historical average and in 2002, the MAP was 329.5 mm, compared with 64% of historical average.

Figure 4: Rainfall and drought analysis by the method of standardized precipitation index.



When we analysed the average rainfall per decade in Yaqui River basin, we found that the MAP reached the highest value of 562.8 mm, in early 1980s fol-lowed by the early 1990s with 533.8 mm. Instead, the MAP of the three years between 2000 and 2002 was 404 mm, only 22% lower than the historical average and 28% lower than average for the 1980s.

4 Drought analysis

4.1 Methods and decisive factors

Analysis of meteorological drought is considered as a basic element of the hydro-logic cycle which determines the runoff channel. To do this, we used a dimension-less index called Standardized Precipitation Index (SPI by its initials in English). This index is a criterion for determining when to consider a certain region to be under drought situation over a period of time [10]. Drought is a complex phenom-enon that is part and parcel of climate events; it is a peculiarity of climate and environment. Droughts are unpredictable and may occur at anytime, anywhere, and we call it the silent risk. Its main features are the duration, severity or accu-mulated defi cit, magnitude and geographic extent. Although the causes of drought are not precisely known, admitted that in general droughts are due to changes in atmospheric circulation patterns, they in turn are caused by the uneven heat-ing of the crust and the masses of water, expressed phenomena such as El Niño (Multivariate ENSO Index/MEI). In addition, the burning of fuels, deforestation, land-use change and anthropogenic activities in general contribute to the alteration of the atmosphere and thus to rainfall patterns.

The SPI is an index developed at the University of Colorado, USA, for moni-toring meteorological drought of any term, based solely on the rain. The SPI is a way of measuring drought that is different from the Palmer drought index (PDI) [11]. Like the PDI, this index is negative for drought, and positive for wet conditions [12, 13]. But the SPI is a probability index that considers only precipitation, while Palmer’s indices are water balance indices that consider water supply (precipitation), demand (evapotranspiration) and loss (runoff) [10, 13, 14]. The SPI is based on the records of rainfall which have a good fi t to the prob-ability density function of Gamma, and the functional parameters with which to make estimates of the amount of rainfall at various levels of probability may be calculated for each case. Defi ned parameters of the Gamma function is rare in actual use; however, it can transform a standard normal function known as Gaussian with zero mean and variance zero. Under this transformation, the mean rainfall for a given period becomes zero or mean value of the standard normal function, and deviations (more or less rain) are represented in terms of standard deviation [15].

In the SPI, given that a continuous record of monthly rainfall values may include zero values, using a computer program the adjustment to the Gamma function are made and then the standard normal function are transformed. Having the index at different timescales, the utility is that we can analyse the behaviour of rainfall in



different periods, as the rainy season from July to September. SPI conventional values to classify the drought are presented in Table 1.

Common to all types of drought is the fact that they originate from a defi ciency of precipitation resulting from an unusual weather pattern, and that is why we used the SPI. If the weather pattern lasts a short time (say, a few weeks or a couple months), the drought is considered short term. But if the weather or atmospheric circulation pattern becomes entrenched and the precipitation defi cit lasts for sev-eral months to several years, the drought is considered to be a long-term drought. It is possible for a region to experience a long-term circulation pattern that pro-duces drought, and to have short-term changes in this long-term pattern that result in short-term wet spells. Likewise, it is possible for a long-term wet circulation pattern to be interrupted by short-term weather spells that result in short-term drought [10].

Taking into account the scientifi c validity of the method, the results obtained from the SPI till October 2010 in the basins of the Sonora and Yaqui, shown in Fig. 4, for periods of 48 months is an indicator of long-term drought, and show a tendency to fi nd hydrological drought. In the Sonora River basin for periods of 48 months shows that during the past 13 years the index had been below 0.0 until reaching critical values of −2.23 and −2.27 in 1999 and 2000, respectively, indicat-ing an exceptional drought. As of December 2009, the index value was −0.14, while for the month of October 2010 the index was −0.3. The graph of Fig. 4 shows how a larger scale values tend to fade and the media, indicating the exis-tence of a meteorological drought for the Sonora River basin, which in recent years has been the most severe and prolonged period with data.

In the Yaqui River basin the results obtained from the SPI till October 2010 for periods of 48 months showed that in the period 1998–2009, the rate was less than −0.5, the threshold for dry weather reaching critical values up to −2.0 in 2003, indicating an exceptional drought. As of December 2009, the index value was −0.60, while for the month of October 2010 the index was −0.44, indicating that it is almost on the edge of the SPI drought classifi cation. It is important to note the trend that shows the SPI from the year 2003, which indicates a recovery in the precipitation. This recovery is refl ected in storage since the system of the Yaqui River dams.

Table 1: Conventional values for drought.

Phase SPI value

Incipient drought −0.50 a −0.79

Moderate drought −0.80 a −1.19

Severe drought −1.20 a −1.49

Extreme drought −1.50 a −1.99

Exceptional < −2.00



5 Tropical cyclones

5.1 Incidence of events

The statistics of Eastern Pacifi c tropical cyclones during the period from 1967 to 2009 indicates that in total there have been 356 hurricanes, of which 132 have been Category 1, 67 Category 2, 63 grade 3, 85 Category 4 and 9 Category 5. Based on the statistics of the years 1949–2009, the incidence of tropical cyclones in the region is presented for the period from 15 August to 15 October. The statistics of tropical cyclones which have affected the study area between 1948 and 2008 shows that of 27 tropical cyclones, 48.1% had attained the status of Hurricane 1 (H1), Tropical Storm (TT) and Hurricane Category 4 (H4) to 18.5% each, and Hurricane Categories 2 (H2) and 3 (H3) with 7.4% each.

In the last decade of the twentieth and early twenty-fi rst centuries, there has been an increase in the incidence of tropical cyclones in the state of Sonora, as well as the incidence review, and 44.4% occurred in these last two decades. That has been well documented in other areas since at least 1900 [16, 18]. And the destructive effects of tropical cyclones have been also most severe in recent years, although in this statistic we are not considering the Tropical Cyclone Jimena, which caused heavy damage in the coastal area of Valle de Guaymas in October 2009, with very specifi c causes analysed by Rangel-Medina et al. [17], but the effects on the water infrastructure, roads and urban areas of the cities Guaymas and Empalme, Sonora were serious but unpredictable. This problem seems to be the tendency in our days, the state of current understanding is such that we should expect hurricane frequ-encies in the future to have a great deal of year-to-year and decade-to-decade variations as has been observed over the past decades and longer [8].

6 Conclusions and recommendations

The use of the SPI was a suitable analysis and tool to fi nd that the basins of the Sonora and Yaqui had a period of drought (1995–2007). The sequence of this drought was as follows: in its initial stage, the weather was dry and characterized by the absence of rainfall amount, intensity and time as well as high temperatures, low relative humidity, more sunshine and less cloud.

We observed agricultural drought, which was characterized by defi cient soil moisture, and manifested by lower or no vegetation development. Due the results hydrological drought was the longest term that can be up for several years. It was basically characterized by a lowering in the runoff of rivers, and reduced volumes in reservoirs and aquifers. In recent years, rainfall recorded is below the historical average, which has been a factor in the low surface runoff and water defi cit in the region and there is no availability of surface water to ensure water supply for different uses that is required the municipality of Hermosillo, Sonora. The SPI indicates a more severe drought in the basin of the Rio Yaqui. However, the runoff volume recovery has been faster in the Yaqui River, due to rainfall.



Rainfall–runoff relation and storage have no signifi cant recovery to allow the entry of water into the dams of the Sonora River basin, the historical average run-off is under the period 1996–2009, indicating a prolonged hydrological drought. On the contrary contributions to the system of the Yaqui River dams have been suffi cient to fi ll the storage vessels, indicating variability between the two basins in the region. The SPI indicates a more severe drought in the basin of the Rio Yaqui in Sonora; however, the runoff volume recovery has been faster in the Yaqui River, due to rainfall.

The main effects of water defi cit were manifested in economic, related to the loss of income and productivity, which implies social and environmental impacts that affect the natural biotic and landscape and that are manifested in a signifi cant reduction of fl ora and fauna. For that reason it is necessary to increase the monitoring; we recommend the improvement of the climatologic and hydrologic gauging stations’ conditions and as soon as possible inte-grate plans and programs to relocate population settled on high risk areas in lowlands [20].

Considering that all these risks are ‘outcome risks’ and integrate considerations of vulnerability with event risk to characterize an event that causes losses, we estimate that in the next decade the north-western region will reach future losses due to extreme events that could reach at least $200 US billion a year. Most of these losses will be charged on the poorer environment (water extremes), loses in agricultural and industrial activities, increasing poverty in the region and dimin-ishing trade markets because of destroying the infrastructure.

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