Assessment of Meteorological Drought Indices Using the Reconnaissance Drought Index (RDI) and Standardized Precipitation Index (SPI) in Duhok City, Northern Iraq

Abstract

Drought is a natural disaster characterized by a deficiency of water resources in a designated territory during a particular period of time. It has a profound effect on several critical facets of life, including environmental, economic, and social activities. Forecasting drought episodes is a crucial component for disaster preparation, mitigating its impact and enhancing efforts to respond. The three parameters, such as frequency, severity, and time period, are essential for the prediction and evaluation of droughts. Two drought indicators, the Reconnaissance Drought Index (RDI) and the Standardized Precipitation Index (SPI), were employed to predict potential drought conditions in Duhok city, Iraq. Forty-three years of climate data (average monthly precipitation and temperature) were utilized over the period from 1980 to 2023, obtained from the Duhok meteorological station. The indices were computed at 3, 6, and 12-month intervals, incorporating the estimation of potential evapotranspiration using the Thornthwaite technique via DrinC tools. The temporal severity and frequency of drought were computed and studied for each drought indicator. Based on  SPI indices the moderately droughts have occurred in years (1999 to 2000, 2007 to 2008, 2008 to 2009, and 2017 to 2018) with a 4-year frequency with 9.30% probability of events. Also, according to RDI indices, the moderately droughts have occurred in years (1999 to 2000, 2001 to 2002, 2007 to 2008, 2008 to 2009, and 2017 to 2018) in 5-year frequency with 11.63%  probability events. However, from both indices, the severe droughts were shown in years (2010 to 2011 and 2022 to 2023) in a 2-year frequency with a 4.65% probability that events occurred. Moreover, the extremely drought was shown in years (2021 to 2022) in a year frequency with 1% probability from each index. The findings of this study indicate that the RDI is more responsive than the SPI to climatic circumstances, thereby emphasizing the importance of evapotranspiration in drought evaluations. The T-test results indicated that both indices exhibit identical behavior depending on P-value is > 0.05; however, the RDI, mainly due to its incorporation of potential evapotranspiration under comparable climatic situations, demonstrates more sensitivity. This research recommends utilizing the RDI index as the appropriate drought index to evaluate drought conditions in water supply management and planning within the study region.