Developing and modeling precipitation duration curves and determining spatial and temporal distributions of precipitation over different percentages of time

Abstract

Determining the temporal distribution of precipitation is of critical importance for engineering hydrology, agricultural yield forecasting, and drought monitoring. The aims of the research carried out in this context were threefold: a) to develop "precipitation duration curves", i.e., PDCs, of long-term total precipitation series, b) to investigate likely mathematical models of PDCs of each meteorological station studied, and c) to determine spatial and temporal distributions of precipitation that occur equalled or exceeded at 50% and 80% of the time. In line with the objectives, the PDCs were developed for each meteorological station. To this end, long-term annual precipitation data series were obtained from a total of 11 meteorological stations located in and around the borders of Sanliurfa province. PDCs of meteorological stations were modelled using the fifth-order regression equation at the 5% significance level. The mathematical forms of the developed model equations were used to predict precipitation amounts for each station at 50% and 80% of the time. The predicted precipitation data were mapped to delineate the spatial distribution of precipitation, and then hypsometric curves were generated from these maps. It was found that the standard errors (SE) of the "precipitation duration curves" models showed an increasing tendency as the standard deviation of the rainfall series increased. Regression analysis results showed that the SE values of the models change in direct proportion to the increase in extreme precipitation values. Considering the amount of precipitation that exceeds or equals 50 per cent of the time, it can be concluded that "Semiarid" climate characteristics prevail in the south of Hilvan meteorological station and "Humid" climate characteristics in the north. The precipitation, which occurs 80% time equaled or exceeded, indicates "Arid" climate characteristics in the southern parts of the Harran district and "Semiarid" climate characteristics in the northern parts of the study area. Considering the area averaged precipitation values corresponding to the two exceeded or equalled the percentage of time ratios, i.e., 50% and 80%, it can be concluded that "Semiarid" climate characteristics are dominant in Sanliurfa province and its surrounding geography.