applying methods for assessing the costs and benefits of cca 2 nd regional training agenda, 30...

Applying Methods for Assessing the Costs and Benefits of CCA

2 nd Regional Training Agenda, 30 September – 4 October 2013

Priyanka Dissanayake- Regional CoordinatorGlobal Water Partnership South Asia

Prof Robert Mendelsohn - Yale UniversityOctober 3, 2013 Bangkok , Thailand

What is Hydrology? What is Hydrology?

– It is a science of water.It is a science of water.– It is the science that deals with the It is the science that deals with the

occurrence, circulation and distribution of occurrence, circulation and distribution of water of the earth and earth’s atmospherewater of the earth and earth’s atmosphere

– Estimation of water resources– The study of processes such as The study of processes such as

precipitation, , evapotranspiration, , runoff and and their interaction

– The study of problems such as The study of problems such as floods and and droughtsdroughts and strategies to combat and strategies to combat themthem

Hydrologic CycleHydrologic Cycle

Water exists on the earth in all its Water exists on the earth in all its three states, viz. liquid, solid, three states, viz. liquid, solid, gaseous and in various degrees of gaseous and in various degrees of motionmotion


Water, irrespective of different Water, irrespective of different states, involves dynamic aspect states, involves dynamic aspect in nature.in nature.

The dynamic nature of water, the The dynamic nature of water, the existence of water in various existence of water in various state with different hydrological state with different hydrological process result in a very process result in a very important natural phenomenon important natural phenomenon

called called Hydrologic cycleHydrologic cycle


Evaporation of water from water bodies, such as Evaporation of water from water bodies, such as oceans and lakes, formation and movement of oceans and lakes, formation and movement of clouds, rain and snowfall, stream flow and ground clouds, rain and snowfall, stream flow and ground water movement are some examples of the water movement are some examples of the dynamic aspects of water dynamic aspects of water


Evaporation from Evaporation from water bodieswater bodies

Water vapor moves Water vapor moves upwardsupwards

Cloud formationCloud formation CondensationCondensation PrecipitatePrecipitate InterceptionInterception TranspirationTranspiration InfiltrationInfiltration Runoff–stream flowRunoff–stream flow Deep percolationDeep percolation Ground water flowGround water flow

Hydrologic CycleHydrologic CycleThe hydrologic cycle has importance The hydrologic cycle has importance influence in a variety of fields agriculture, influence in a variety of fields agriculture, forestry, geography, economics, forestry, geography, economics, sociology, and political scene sociology, and political scene Engineering application of the knowledge Engineering application of the knowledge are found in the design and operation of are found in the design and operation of the projects dealing with the projects dealing with water supplywater supply, , hydropower, irrigation & drainage, flood hydropower, irrigation & drainage, flood control, navigation, coastal work, various control, navigation, coastal work, various hydraulic structure works, salinity control hydraulic structure works, salinity control and recreational use of waterand recreational use of water

Catchment area/WatershedCatchment area/Watershed

The area of land draining in to a The area of land draining in to a stream or a water course at a given stream or a water course at a given location is called location is called catchment area / catchment area / drainage area / drainage basin / drainage area / drainage basin / watershedwatershed..

A catchment area is separated A catchment area is separated from its neighboring areas by a from its neighboring areas by a ridge called ridge called divide / watersheddivide / watershed

Watershed and watershed divideWatershed and watershed divide

Watershed/ catchment

Watershed/ catchment

Watershed divide

Watershed & Watershed & Water Budget EquationWater Budget Equation

A watershed is a geographical unit in which A watershed is a geographical unit in which the hydrological cycle and its components the hydrological cycle and its components can be analyzed. can be analyzed. Usually a watershed is defined as the area Usually a watershed is defined as the area that appears, on the basis of topography, to that appears, on the basis of topography, to contribute all the water that passes through contribute all the water that passes through a given cross section of a streama given cross section of a streamThe equation is applied in the form of water-The equation is applied in the form of water-balance equation to a geographical region, in balance equation to a geographical region, in order to order to establish the basic hydrologic establish the basic hydrologic characteristics characteristics of the region. of the region.

Water Budget Equation Water Budget Equation For a given catchment, in an interval of For a given catchment, in an interval of

time time ∆t, the continuity equation for ∆t, the continuity equation for water in its various phases can be given water in its various phases can be given as:as:Mass inflow – Mass outflow = change in mass storageMass inflow – Mass outflow = change in mass storage

(in soil or bedrock)(in soil or bedrock)

If the density of the inflow, outflow and If the density of the inflow, outflow and storage volumes are the same:storage volumes are the same:

VVi i - - Inflow volume in to the catchment, VInflow volume in to the catchment, Vo o - Outflow - Outflow

volume from the catchment and volume from the catchment and ∆S -∆S - change in the change in the water volume water volume

Water Budget Equation Water Budget Equation Therefore, the water budget of a Therefore, the water budget of a

catchment for a time interval catchment for a time interval ∆t is ∆t is written as:written as:

P – R – G – E – T = ∆SP – R – G – E – T = ∆SP = Precipitation, R = Surface runoff, G = net ground water flow P = Precipitation, R = Surface runoff, G = net ground water flow

out of the catchment, E = Evaporation, T = Transpiration, and out of the catchment, E = Evaporation, T = Transpiration, and ∆S = change in storage ∆S = change in storage

The above equation is called The above equation is called the water the water budget equation for a catchment budget equation for a catchment

The purpose of the water balanceThe purpose of the water balance is to is to describe the various ways in which describe the various ways in which the water supply is expendedthe water supply is expended

Components of hydrologic Components of hydrologic cyclecycle

Precipitation

Infiltration

Evapo transpiration

Inter flow

Groundwater flow

Base flow

Stream flow

(Runoff)

Data for collection

Climate Model & Input Data

• Predicts precipitation by month in watershed–Hourly precipitation if tracking floods

• Predicts temperature by month• Land cover over watershed is an input• Land cover and temperature used to

predict monthly evapotranspiration• Snow and ice can hold (store) water

depending on temperature • Precipitation, evapotranspiration, and

change in snow and ice determines flow

Water supply per person for individual river basins as of 1995 WRI

water supply per person for individual river basins projections for 2025 WRI

www.iwmi.org

Water for a food-secure world

Observed Changes

Increases in some places and decreases in others

No clear trend

Trend in Annual Runoff, 1971-1998 as a % of 1900-1970 Average reconstructed by climate models

Source: Milly et al. 2005

www.iwmi.org

Water for a food-secure world

Projected Changes

Change in Annual Runoff in 2090-2099 relative to 1980-1999

Positive: Sri Lanka, Bangladesh, India, parts of Nepal and Bhutan

Negative: Pakistan and Afghanistan

Source: Milly et al. 2005