Probable maximum precipitation estimation for the catchment area (A case study of the Tuul River basin, Mongolia)

Сав газрын түвшинд боломжит хамгийн их хур тунадсыг тооцох нь (Туул голын сав газрын жишээн дээр)

Abstract

The particular study covers estimation of daily maximum rainfall amount, namely by estimating the probable maximum precipitation, by some selected methods and prediction of future trends of rainfall amount and location. The daily maximum rainfall amount with different return period is one of the key inputs  for any flood estimation studies.  The study also contributes to reduction of risk of flood disasters in river basins with high density of population  and infrastructural facilities.  In these studies have been used series of daily maximum rainfall data at 21 meteorological stations in the Tuul river basin for last thirty years (1991-2020) and the statistical method of Hershfield was applied for the analysis and results of the estimation are compared with the actual observed values. The study results that mean difference between estimated values by the Hershfield statistical method with observed one was around 11mm by reaching highest values difference to 51 mm and lowest difference was even smaller than 2 mm in the daily maximum rainfall. The Nash-Sutcliffe coefficient between estimated and observed values was 0.90, which indicates strong correlation rate of the estimation. Another goal of this study was to evaluate spatial distribution of the PMP within the Tuul river basin. By analyzing set of data from 21 weather stations 630 occurrence data, we obtained the estimated daily maximum values of PMP in the Tuul river as mean of 108.8 mm. In this research, we also have used the CNRM-CM6-1-HR (France) model which initiated and developed by World Climate Research Program (WRCP) with the highest spatial resolution of 0.50x0.50 for estimation of rainfall amount during period of 1991-2014 and the analysis showed reasonable high values of correlation coefficient as 0.60. The data series of 1991-2014 is recommended and used in The Sixth Assessment Report-AR6, developed by the Intergovernmental Panel on Climate Change (IPCC) of the United Nations Framework Convention on Climate Change. Finally, the results of the analysis by CNRM-CM6-1-HR (France) model showed that probable maximum precipitation (daily maximum rainfall) is expected to be around 110 mm in the basin for period of till 2099.