Preliminary Development of the Water Evaluation and Planning (WEAP) Tool for the Chira-Piura Watershed in Peru

The watershed is comprised of two major river basins, the Piura River watershed (10970 km2) and the Chira River watershed (17840 km2). The majority of the water in these two basins is utilized for irrigated agriculture and to satisfy urban demands in the lower arid coastal plains in the west of the region. A number of WEAP models have been constructed in the region in the past, but none of them have represented the hydrology, infrastructure, and demands of the Chira-Piura watershed in a comprehensive manner. Therefore, the goal of this modeling effort is to construct a calibrated monthly time-step model with sufficient spatial resolution to aid in the evaluation of potential climate change adaptation strategies. The WEAP model will be used to support a robust decision-making process that can be used to identify and justify projects for climate adaptation funding. The model will also provide basin planners and water users with an interactive tool to aid future water management planning and decision making. The WEAP model will be constructed using a period of about twenty years (1972-1992) as the calibration period. Historic climate data, including precipitation, temperature, and humidity, will be used as input to the rainfall-runoff routines contained within the WEAP catchment objects. The model will be run again using climate change projections as input to assess the potential impacts on water management and the performance of adaptation strategies. Various methods of processing historic records have been employed to extend historic values to areas within the basin where records do not exist. Simple regressions between elevation and temperature have been used to estimate temperatures at any point on the digital elevation map. Inverse distance weighting has been used to interpolate between available historical observations to obtain maps of precipitation variation across the basin. The WEAP model will be used to guide the calibration process, starting from the uppermost regions of the watershed and working downwards until the low-lying coastal plains are reached. The model will be updated with the best data and expert knowledge available through the WEAP model building process, which is being reviewed and vetted by the Modeling Team within the Modernization Group. The WEAP model will be useful in the preparation of the Climate Change scenarios to review the spatial and temporal scales at which the scenarios need to be developed for this particular region. The scenarios prioritized during the Experimental Design and Training, such as the páramo conservation uncertainty and the improvement in irrigation efficiency strategy, will be included in the structure of the model. The construction of a WEAP model that represents the water system within the Chira-Piura watershed is a key objective of the PARA-Agua project in Peru. The model will be used to support a robust decision-making process that can be used to identify and justify projects for climate adaptation funding. The model will also provide basin planners and water users with an interactive tool to aid future water management planning and decision making. The PARA-Agua project has already constructed a WEAP application that focuses on the hydrologic and water management conditions in the Peruvian portion of the upper Chira River watershed. This highly detailed model has been integrated into the existing official WEAP model and its hydrologic routines are being used to guide the development of the rainfall-runoff routines for the rest of the Chira-Piura watershed. The WEAP model will be constructed using a period of about twenty years (1972-1992) as the calibration period. Historic climate data, including precipitation, temperature, and humidity, will be used as input to the rainfall-runoff routines contained within the WEAP catchment objects. The