Catchment water yields, calculated by M. Turc technique, having probability levels of 50%, 80% and 90% are used for the design of reservoir capacity of small earthen dams. This study aims to figure out the suitable probability levels to be used for the design of reservoirs of small earthen dams lying in drought-prone areas. After having performed frequency analysis technique on the yearly total precipitation series of each meteorological station, precipitations values with 50%, 80% and 90% probability levels were estimated for each meteorological station. By using precipitations at 50% probability level, precipitation threshold values corresponding to Percent of Normal Precipitation Index (PNI) drought categories of 65%, 75% and 85% were calculated for each station. These precipitation values were mapped in Geographical Information Systems (GIS) media by employing Ordinary Cokriging interpolation technique; then, runoff maps of M. Turc method were generated accordingly. Hypsometric curves of runoff values were developed for each runoff case. It was determined that hypsometric curves for 80% and 90% probability levels overlapped quite well with the curves of PNI drought category of "Mild Drought" and "Moderate Drought", respectively; and hypsometric curve of M. Turc runoff values with 50% probability level represented the curve relating to the runoff threshold values for PNI drought category of "Normal and Over, i.e. No Risk". Consequently, the use of M. Turc runoff values with 50% probability level was not found suitable for the capacity design of small earthen dams lying in the Seyhan River Basin prone to drought risk. Hence, it was suggested that runoff calculation for the design of reservoirs of small earthen dams should be done by using precipitation data having 80% or 90% probability levels in order to reduce construction costs.