Applying Methods for Assessing the Costs and Benefits of CCA 2 nd Regional Training Agenda, 30 September – 4 October 2013 Priyanka Dissanayake- Regional Coordinator Global Water Partnership South Asia Prof Robert Mendelsohn - Yale University October 3, 2013 Bangkok, Thailand

What is Hydrology? –It is a science of water. –It is the science that deals with the occurrence, circulation and distribution of water of the earth and earth’s atmosphere –Estimation of water resources Estimation of water resourcesEstimation of water resources –The study of processes such as precipitation, evapotranspiration, runoff and their interaction precipitationevapotranspirationrunofftheir interaction precipitationevapotranspirationrunofftheir interaction –The study of problems such as floods and droughts and strategies to combat them floods

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

Hydrologic Cycle Water, irrespective of different states, involves dynamic aspect in nature. Water, irrespective of different states, involves dynamic aspect in nature. The dynamic nature of water, the existence of water in various state with different hydrological process result in a very important natural phenomenon called Hydrologic cycle The dynamic nature of water, the existence of water in various state with different hydrological process result in a very important natural phenomenon called Hydrologic cycle

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

Hydrologic Cycle Evaporation from water bodies Evaporation from water bodies Water vapor moves upwards Water vapor moves upwards Cloud formation Cloud formation Condensation Condensation Precipitate Precipitate Interception Interception Transpiration Transpiration Infiltration Infiltration Runoff–stream flow Runoff–stream flow Deep percolation Deep percolation Ground water flow Ground water flow

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

Catchment area/Watershed The area of land draining in to a stream or a water course at a given location is called catchment area / drainage area / drainage basin / watershed. The area of land draining in to a stream or a water course at a given location is called catchment area / drainage area / drainage basin / watershed. A catchment area is separated from its neighboring areas by a ridge called divide / watershed A catchment area is separated from its neighboring areas by a ridge called divide / watershed

Watershed and watershed divide Watershed/ catchment Watershed divide

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

Water Budget Equation For a given catchment, in an interval of time ∆t, the continuity equation for water in its various phases can be given as: For a given catchment, in an interval of time ∆t, the continuity equation for water in its various phases can be given as: Mass inflow – Mass outflow = change in mass storage (in soil or bedrock) (in soil or bedrock) If the density of the inflow, outflow and storage volumes are the same: If the density of the inflow, outflow and storage volumes are the same: V i - Inflow volume in to the catchment, V o - Outflow volume from the catchment and ∆S - change in the water volume

Water Budget Equation Therefore, the water budget of a catchment for a time interval ∆t is written as: Therefore, the water budget of a catchment for a time interval ∆t is written as: P – R – G – E – T = ∆S P = Precipitation, R = Surface runoff, G = net ground water flow out of the catchment, E = Evaporation, T = Transpiration, and ∆S = change in storage The above equation is called the water budget equation for a catchment The above equation is called the water budget equation for a catchment The purpose of the water balance is to describe the various ways in which the water supply is expended The purpose of the water balance is to describe the various ways in which the water supply is expended

Components of hydrologic cycle 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

Water for a food-secure world Observed Changes Increases in some places and decreases in others No clear trend Trend in Annual Runoff, as a % of Average reconstructed by climate models Source: Milly et al. 2005

Water for a food-secure world Projected Changes Change in Annual Runoff in relative to Positive: Sri Lanka, Bangladesh, India, parts of Nepal and Bhutan Negative: Pakistan and Afghanistan Source: Milly et al. 2005