Document Type : Research Article
Authors
1 Academic Center for Education, Culture, and Research , ACECR, , Lorestan, Iran
2 Graduated in Water Structures, Faculty of Agriculture, Lorestan University
3 PhD in Climatology, Department of Geography, Kharazmi
4 Professor of Climatology, Faculty of Geographical Sciences, Kharazmi University, Tehran, Iran
Abstract
Introduction:
Precipitation is a key climate variable that is very difficult to predict in numerical weather models. Since precipitation in mountainous areas may vary greatly in the spatio-temporal dimension, accurate spatially distributed data are very important for assessing water resources in mountainous areas.The large temporal and spatial changes of precipitation, especially in mountainous areas, have turned it into a controversial variable in climate models. Measuring precipitation (rain and snow) along with its distribution and changes is very important to improve our understanding of global water cycle and energy, water resources monitoring, hydrological modeling. Lack of reliable data is one of the most important challenges in rainfall analysis. Since precipitation in mountainous areas varies greatly in the temporal-spatial dimension, accurate spatially distributed data is very important for water resources assessment and management. However, in many mountainous regions, few rain gauge stations are available. Today, satellite products are used as a tool to measure precipitation in these areas, but the difference between the existing products challenges their accuracy for mountainous areas. On the other hand, the quality of different satellite products varies from one product to another and from one climatic region to another Therefore, there is a need to fully evaluate them before using them.
Method:
The purpose of this research is to evaluate the precipitation data of two satellite products (GPM, PERSIAN) and reanalysis data (ECMWF) in the estimation of precipitation in mountainous areas without stations in Lorestan province. In the present study, the rainfall data of 24 synoptic and rain gauge stations with appropriate distribution in Lorestan province were selected with emphasis on the stations located or close to the mountainous areas. from rainfall data (daily, monthly and yearly) of GPM and PERSIANN satellites and reanalysis data (ECMWF) (period 2021-2015) and synoptic and rain gauge stations (period 2021-2015) in Lorestan province to evaluate satellite precipitation algorithms and estimate The amount of precipitation in the areas without statistics was used.
To evaluate the accuracy of the products, R-squared correlation (R2), root mean square error (RMSE), standard deviation (MAD), correlation coefficient (R), error deviation (MBE) and Nash-Sutcliffe coefficient (NS) were used. Also, the probability of detection (POD), false alarm ratio (FAR), and critical success index (CSI) indices were used to validate the data.
The results of the review of all three products (GPM, PERSIAN, ECMWF) showed that in general all three products are not accurate enough in estimating daily rainfall, although a few stations have medium to low correlation coefficients, but the ability to estimate rainfall due to the existence of other There are no errors. In general, ECMWF products are more reliable than other products on a daily scale. Precipitation estimation using satellite data on a monthly scale indicated that these products provide favorable results for estimating precipitation on a monthly scale. Among the three products, with different data, the GPM satellite product has better accuracy with regard to the amount of errors and also the spatial pattern of the estimated precipitation. On an annual scale, considering the amount of statistical errors as well as the spatial patterns of average annual precipitation, GPM satellite has a better ability to estimate the amount of precipitation. Also, according to the results of the MBE index on a daily and monthly scale, ECMWF products are overestimated and PERSIAN and GPM products are underestimated in precipitation estimation. In the annual scale, GPM and ECMWF products are overestimated and PERSIAN products are underestimated.. Based on the observed rainfall of the studied stations, the highest rainfall occurs in the west and center of the studied area, and the eastern parts of the area have the lowest amount of rainfall. In the ECMWF satellite product, the spatial pattern of the amount of precipitation has changed with the displacement of precipitation cores to the west and east of the region, which is different from the climatic reality of the studied region. In the product of the PERSIAN satellite, the precipitation cores are closer to the reality by moving towards the center and north, but it is still different from the climatic reality of the region. In the GPM satellite product, the spatial pattern of the annual rainfall amount is almost similar to the spatial pattern of observed rainfall, and the precipitation cores are identified in the center and west of the region; Therefore, according to the spatial pattern of annual rainfall, GPM satellite products have better accuracy than other products.
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