SPDSS_Task53-3_Assign Key Climate Information to Irrigated Acreage and Reservoirs

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models in the SPDSS, and provides a more continuous interpolation of the point values available for the climate station data than the Thiessen polygon method. Once the grid network is developed, it can be applied to any point location or summarized for a polygon area whereas with kriging, the locations must be determined beforehand. Note that both the linear interpolation and kriging methods may require an orographic adjustment, applied to the actual climate data, if used over areas with elevations outside the range of the climate station coverage. The linear interpolation method was applied to develop a grid network for key climate stations east of the foothills that include the entire GW model area and the majority of irrigated acreage. For the irrigated acreage in the SPDSS, the vast majority of lands are at an elevation of less than 6,500 feet and have adequate coverage of climate stations without the need for elevation adjustment. Higher areas of the groundwater model may require an orographic precipitation adjustment to the climate station data to accurately estimate precipitation recharge. This orographic adjustment to precipitation data is described below. This network of climate station grids was then used to create a uniform coverage of climate station weights. The coverage will be used to automate the assignment of appropriate key climate stations and weights for estimating consumptive use at any point or area (parcels, groups of parcels, grid cells, etc) located in their respective study areas. In order to extrapolate climate station weights to the limits of the study area and to those areas up to 6,500 feet, the locations of climate stations from outside the state and above 6,500 feet were utilized to create a network of grids. After this analysis, the weights from climate stations outside the state or above 6,500 feet were set to zero and the remaining weights prorated upward to assure a total value of 1.0. This maintains the requirement of insuring the sum of the climate station weights equal to one, and also avoids utilizing climate station data outside the state not currently stored in HydroBase. In the foothills and higher elevations, climate stations were assigned to reflect climate conditions by sub-water district. Figure 1 shows the division of water districts along the foothills with the upper and lower designations. Figure 1 was developed using digital elevations obtained from the State, originally derived from data obtained from the USGS. Table 1 presents the upper water district climate stations that should be used in the consumptive use model. Page 4 of 11