Spatial variations of water loss during drought: A case study

A regional water conservation system for drought management involves many u ncertain factors. Water received from precipitation may stay on the ground surface, evaporate back into the atmosphere, or infiltrate into the ground. Reliable estimates of the amount of evapotranspiration and infiltration ar e not available for a large basin, especially during periods of drought. By applying a geographic information system, this study develops procedures t o investigate spatial variations of unavailable water for given levels of d rought severity. Levels of drought severity are defined by truncated values of monthly precipitation and daily streamflow to reflect levels of water a vailability The greater the truncation level, the lower the precipitation o r streamflow. Truncation levels of monthly precipitation are recorded in de pth of water while those of daily streamflow are converted into monthly equ ivalent water depths. Truncation levels of precipitation and streamflow tre ated as regionalized variables are spatially interpolated by the unbiased m inimum variance estimation. The interpolated results are vector values of p recipitation and streamflow at a grid of points covering the studied basin. They are then converted into raster-based values and expressed graphically . The image subtraction operation is used to subtract the image of streamfl ow from that of precipitation at their corresponding level of drought sever ity. It is done on a cell-by-cell basis resulting in new attribute values t o form the spatial image representing a spatial distribution of potential w ater loss at a given level of drought severity.