Abstract:

Water allocation for the management of droughts is involved with many uncertain factors. One of the most uncertain elements is the amount of evaporation during time periods of drought for a large basin where there is still no reliable estimation. By applying the geographic information system, this study developed the procedure to form the image to express the unavailability of water during periods of drought for a selected drainage basin. Gaging stations of precipitation and streamflow in the studied basin were selected to spatially represent the area. Based on the method of truncation level, 70, 80, 90, and 95% truncated values of precipitation and streamflow were estimated at each gaging station. A 70% truncation level means that 70% of historic records at the corresponding gaging location were greater than the truncated value. The greater the truncation level, the lower the availability of precipitation or streamflow. Hence, these truncation levels were used to reflect the levels of drought severity. It is noted that precipitation was recorded by the depth of water and streamflow was expressed by the equivalent water depth. Since hydrologic records were taken at gaging locations, truncation levels of precipitation and streamflow were location-dependent variables. Assuming that these truncation levels at all gaging locations are regionalized variables, the kriging method was applied to estimate their regional distribution. The analysis of kriging, a spatial interpolation technique, was based on the minimum variance unbiased estimation. The kriging analysis of these truncation levels yielded vector values of precipitation or streamflow for a grid of points covering the studied drainage basin. These point values were converted into a grid of raster-based values and were expressed by a spatial image. The mathematical function of subtraction was used to subtract the streamflow image from the precipitation image for each level of drought severity. These were done on a cell-by-cell basis to create new attribute values for the new image to represent the unavailability of water at each corresponding level of drought severity.

1. Professor, Civil Engineering Department, Ohio University, Athens, OH 45701.

2. Former Graduate Student, Civil Engineering Department, Ohio University, Athens, OH 45701.

3. Former Graduate Student, Civil Engineering Department, Ohio University, Athens, OH 45701.

Proceedings of the First Federal Interagency Hydrologic Modeling Conference
April 1998

For more information on this or any other paper contact Terry Chang by email at tjchang@bobcat.ent.ohiou.edu