Assessment of Precipitation Estimation from the NWP Models and Satellite Products for the Spring 2019 Severe Floods in Iran

Aminyavari Aminyavari,Sharifi Sharifi,Saghafian Saghafian

doi:10.3390/rs11232741

Abstract

Precipitation monitoring and early warning systems are required to reduce negative flood impacts. In this study, the performance of ensemble precipitation forecasts of three numerical weather prediction (NWP) models within the THORPEX interactive grand global ensemble (TIGGE) as well as the integrated multi-satellite retrievals for global precipitation measurement (GPM), namely IMERG, for precipitation estimates were evaluated in recent severe floods in Iran over the March–April 2019 period. The evaluations were conducted in three aspects: spatial distribution of precipitation, mean areal precipitation in three major basins hard hit by the floods, and the dichotomous evaluation in four precipitation thresholds (25, 50, 75, and 100 mm per day). The results showed that the United Kingdom Met Office (UKMO) model, in terms of spatial coverage and satellite estimates as well as the precipitation amount, were closer to the observations. Moreover, with regard to mean precipitation at the basin scale, UKMO and European Center for Medium-Range Weather Forecasts (ECMWF) models in the Gorganrud Basin, ECMWF in the Karkheh Basin and UKMO in the Karun Basin performed better than others in flood forecasting. The National Centers for Environmental Forecast (NCEP) model performed well at low precipitation thresholds, while at high thresholds, its performance decreased significantly. On the contrary, the accuracy of IMERG improved when the precipitation threshold increased. The UKMO had better forecasts than the other models at the 100 mm/day precipitation threshold, whereas the ECMWF had acceptable forecasts in all thresholds and was able to forecast precipitation events with a lower false alarm ratio and better detection when compared to other models.

Highlights

In recent decades, observed climate trends have shown an increase in temperature worldwide so that extreme precipitation has increased in some specific areas [1,2,3,4,5]
The results showed that all of the products could generally capture the main features of the precipitation system, including the spatial distribution, total accumulation, and extreme values (Figure 2)
All of the products were examined in comparison with the in situ observations in three major basins that were most affected by the floods

Summary

Introduction

In recent decades, observed climate trends have shown an increase in temperature worldwide so that extreme precipitation has increased in some specific areas (e.g., eastern half of North America, Eastern Europe, Asia, and South America) [1,2,3,4,5]. These waves deposit the momentum transported, disturbing the stratospheric polar vortex, which can lead to a breakdown of this circulation with the potential to significantly impact the troposphere in mid- to late-winter and early spring [6,7]. Iran’s climate is generally semi-arid and is subject to frequent flooding, causing major damage to people and society. The first flood event occurred in late winter to early spring 2019 in the northeastern provinces due to heavy precipitation over the March 17–22 period. The subsequent second and third flood events occurred in the March 24–26 and March 31–April 2 periods, respectively, where most of the precipitation fell in the southwest, causing widespread damage to the people and infrastructure while filling/causing an overflow of most reservoirs. Studies on the causes of the March–April 2019 severe floods are still ongoing, exceptional precipitation and climate change attribution are on the minds of most experts

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Discussion

Conclusion