examining the coupled effects of land use and climate change ver 1

Examining the coupled effects of land use and

climate change on watershed functions:

experiences from Asia and AfricaJohn M. Gathenya Xing Ma

Jianchu Xu Meine van Noordwijk

Flow at watershed outlet is determined by multiple factors

Land cover / vegetationLand managementSoils and GeologyRainfall Climate / WeatherTopographyDrainage patternWatershed shape

• Climate change Land use changeLess reliable

rainfallLonger dry spells

More ‘extreme events’More demand and less supply of ‘buffer

functions’ in our watersheds; increasing buffer capacity will reduce vulnerability and enhance

adaptation

Increased drainage

Soil compactionLess macropores

Watershedfunctions

1. Transmit water

2. Buffer peak rain events

3. Release gradually

4. Maintain quality

5. Reduce mass wasting

Site cha-

racteristics

• Rainfall• Land

form• Soil

type• Rooting

depth (natural vegetation)

Relevantfor

• Downstream water users,

• esp. living in floodplains & river beds,

• esp. without storage

• or purification

• at foot of slope

Definitions• Buffering capacity of a watershed is

its ability to reduce variation in streamflow relative to rainfall

• Flow persistence is the fraction of flow on the previous day that can be expected as minimum volume of river flow on a given day

Role of RHA tools• Builds on the concept of PRA but

incorporates the use of computer-based hydrological models to:– Find how severe problems are and their

relationship to land use– Find specific land use practices that can

reduce the problem – Establish the potential for RES to

support beneficial land uses– Compare LEK and MEK– Model scenarios of land use

GenRiver modelGeneric river flow model.Distributed process-based model spatial scale: 1-10km2, temporal scale: dailyIs a patch level representation of daily water balance.From each patch, the flows are routed to the outlet.Can be used to study the relationship between land use/management and flows.

FlowPer model• Models, even simple ones like

Genriver are over-parameterized• FlowPer can serve two functions:

– (1) summarize the key parameters that downstream stakeholders can observe on the flow pattern,

– (2) serve as a parsimonious (parameter-sparse)“null model”

– Extract as much information about upstream conditions from the flow data

FlowPer model

Qt+1 = fp Qt + Qadd

Where Qt and Qt+1 are river flows on subsequent days, fp is flow persistence factor (0<fp<1) and Qadd is a random variate reflecting input from recent rainfall

∑Qadd i = (1-fp) ∑Q

Ideally buffered: fp=1, Qadd = 0

Poorly buffered, erratic: fp=0

Can fp be used to indicate watershed quality?

Case Study: Jangkok sub-watershed, Lombok, Indonesia

Gura river

FAO Land cover

SOTER Soils database version 1

4AD01 is 441.9 km2.Rainfall and flow data 6 years 1970-1975 Mean monthly ET values

Genriver / FlowPer results - Gura river

Simulated and observed flows at 4AD01

Flow persistence from FlowPer model

Flow hydrographs from GenRiver model

Gura FlowPer results

High quality flow data required for application of FlowPer

GenRiver application in Mara River basin

Satellite image analysis showed forest in MRB has declined by almost 60% over the 25 years between 1975 and 1999

Amala and Nyangores

Using Genriver, two scenarios were tested in Amala and Nyangores: 1. base case 2. complete forest coverResult: Restoring forest cover may not necessarily increase water yield

Mara river basin

SWAT and FlowPer application Nyando basin, W Kenya

3587 km2

Rain: 800-160030 yrs records

Mean ET from Kericho and Kisumu met

Flow simulated with SWAT model

18 Scenarios

Flow persistence, base case

For Nyando basin, the inter-annual variability in rainfall causes a lot of variability in flow persistence

Flow persistence for changed rainfall and land use conditions – R. Nyando

Mean flow and Flood frequency River Nyando

Climate change, land surface infiltration and mean flow

Land use impact on flood frequency

+10% rain, land use and flood frequency

Flow persistence under changing rainfall

Flow persistence increases with rainfall

Flow persistence higher for improved surface infiltration

When surface infiltration is low, of flow persistence does not seem to respond to change in rainfall

GenRiver for Kapingazi river catchment

• On the southern slopes of Mount Kenya, Area 61 km2

• Is in Upper Tana River Basin• Average annual Rainfall ranges

between 1200 mm and 1800mm• Rainfall data 1976-1994, some

limited flow data for the same period, water permit records.

• Mean monthly ET for Embu KARI station

• SOTER soil DB, digital DEM, satellite derived land cover

Kapingazi ...in good times

Supplies Embu town with a portion of the water consumed and a number of community and individual irrigation and domestic water projects

History of drying up 1984, 2000, 2011

Decreased flows attributed to decreased rainfall, increased water demand, planting of eucalyptus, poor water allocation, farming on river banks and illegal extractions

Kapingazi cacthment

Rainfall at Embu town and Irangi Forest

No discernible trend in mean annual rainfall totals 1978-2008

Farmers say that the rainfall patterns are changing

1st rain season totals decreasing, 2nd rain season totals increasing, annual means remaining constant

Genriver model results – Kapingazi hydrograph 1976-1994

45 flow measurements spread over the period were used to guide the calibration, some points fit, others do not

Statistic Discharge, m3/s

Qmean 1.457

Normal flow, Q80 0.461

Reserve flow, Q95 0.241

In some extreme dry years, e.g. 1984, actual abstractions exceed low flows at outlet. This explains why the flow in Mar/April 2011 also reached zero

Kejie Watershed

• The Kejie watershed occupies a total area of 1755 km2

• The watershed provides ES to Baoshan Prefecture in Yunnan and to Myanmar and Thailand downstream

• Land use classes: forest, grassland, cropland, settlement, barren and water

Kejie watershed

Kejie watershed

• Elevation oranges from 963 to 3076 m.

• In the 40 years, dramatic change in land cover, gradual increase in temperature, no trend in mean annual rainfall, change in rainfall for some months

Kejie watershed Scenarios

• Temperature: T+1, T+2, T+3, T+4 • Rainfall: P-10, P-5, P+5, P+10 • Land cover: forest+, grassland+, crop+,

urban+

Land use change and water balance

Climate change and Q and ET

Land use change and Water balance

Land use change and climate change

ConclusionsIssue to be analysed SWAT GENRIV

ERFLOWPER

Water flows and land use √√√ √√√

Water flows and Agroforestry √ √√

Water flows and land management practices

√√√ √

Soil erosion and land use / management √√√

Peak flow buffering / flow persistence √ √ √√√

User friendly (input data, running), rapid

√√√ √√√

Large complex watersheds √√√GenRiver a good hydrological model for rapid assessment of small watersheds for PES

Conclusions• Impacts of climate change on

watershed functions interact with those of land use change: They may reinforce or weaken each other.– Both should be considered together in

order to identify interactions • Single effects of land cover change

tend to be greater than single effects of climate change...in some cases, effect of inter-annual variability of rainfall is even greater

Reference• van Noordwijk M, Widodo RH, Farida A,

Suyamto DA, Lusiana B, Tanika L and Khasanah N. 2011. GenRiver and FlowPer: Generic River Flow Persistence Models. User Manual Version 2.0. . Bogor. World Agroforestry Centre - ICRAF, SEA Regional Office. 119 p.

•http://www.worldagroforestry.org/sea/publication?do=view_pub_detail&pub_no= MN0048-11

A frog likes water...but not

when it is boiling