BASIN SCALE WATER INFRASTRUCTURE INVESTMENT EVALUATION CONSIDERING CLIMATE RISK Yasir Kaheil Upmanu Lall C OLUMBIA W ATER C ENTER : Global Water Sustainability Initiative Key points Given the environmental impacts and poor socio-economic performance of large storage and canal projects there is a considerable movement against the construction of new large dams and irrigation projects. Watershed management == small is beautiful is being advocated and many successes are demonstrated, but in some cases downstream impacts are also reported. Can a mix of these projects strategically designed in combination with recommended crop choices be effective? Equity, economic efficiency and resilience to climate? An exploration of some of these issues is presented using a simple model Water Infrastructure for Agriculture Surface Water - Large Dam/Canal System High capital cost, High climate resilience, low coverage, inequitable Surface Water - on-farm surface storage Low individual cost, low climate resilience, high coverage Groundwater on-farm wells High operating cost, high climate resilience, site specific coverage, complex equity IWRM how to evaluate integrated effect? Van der Zaag and Gupta (2008) characterization of reservoir social ecology Large Dam + canal system Distributed Storage and aquifer pumping Monitoring & system control Network Simulator to help Integrated Investment & Demand Management including crop choice (space and time), climate, and market forecasts Simulation Model to Investigate performance of mix of central+ decentralized storage Assumptions: Prescribed specific locations and sizes of large reservoirs and canals River basin is divided into subcatchments, each of which has a specified irrigation area whose attributes are considered homogeneous Specify % of irrigable area to use for water collection and height of associated impoundment Optimize crop choice over the basin for the decentralized system such that income equity is achieved Model structure DEM sub-basin and drainage network delineation Stochastic Weather Generator Climate Model or Historical Surface Soils data Crop choices and parameters Economic parameters Storage and conveyance parameters Rainfall-runoff Flow routing Storage water balance model Crop yield model Economic Model Performance assessment Performance Measures van der Zaag and Gupta (2008): The residence time of water in a reservoir: used as a proxy for the spatial scale of the catchment area, and hence of the biophysical impact of the reservoir The water provision capacity: Relative to water supply or population measures, this is used as an indicator of the size of the demand that may be supplied Cost effectiveness of providing reliable access to water per beneficiary: this is an economic efficiency measure computed over the service area The number of beneficiaries and loser compensation: this adds an equity dimension. Performance measures Lall and Kaheil (2009) Equity in terms of irrigation water provided per unit area at a given reliability across the river basin Equity in terms of net income generated per unit area across the river basin Economic efficiency in terms of the net annual income generated per unit total annualized public (and private) investment. Resilience of the system to climate variability. This is measured by the duration and severity of the aggregate failure of the system relative to a specified cropping pattern and spatial distribution of use, and target reliability. Reliability relative to design reliability in the climate change scenario relative to base climate scenario Andhra Pradesh watershed Central Reservoir Canals Skewed rainfall distribution with marked inter-annual and seasonal variability Scenarios Base Climate (historical data) = 30 years Climate Change = 30 years Base Climate Temperature +2 C Base Climate Precipitation Variance increase by 10% Decentralized System Only Specify impoundment height and % land allocation for collection Optimize for crop choice and then use for all others Centralized only Centralized + decentralized Achieving equity: Impact of changing crop choice by location on average annual net income Only Decentralized: Impact of Climate change Scenario: Income distribution Centralized+decentralized storage system: Base vs CC Income impact Summary Opportunities exist for using crop choice to improve economic equity and efficiency in the use of investments for irrigation demand management. There may be cases in which large storage systems can still dramatically outperform (in theory) in delivering economic returns to a select few while improving climate resilience. Small storage systems improve over no irrigation and can be a part of the regional development plan without necessarily a large impact on the performance of the large centralized system