# Exploring the Evolution of Drought Characteristics in Balochistan, Pakistan
## 1 Introduction  
Of all the hazards that wreak havoc across the globe, droughts are perhaps the least understood and the most damaging [1]. Caused primarily by an anomaly in the natural rainfall pattern of a region, droughts have evolved considerably in recent decades due to climate change, which has led to changes in the hydrometeorological processes throughout the Earth. Global warming has caused the average surface temperatures to increase, leading to changes in rainfall patterns, increased evapotranspiration, and shifting cropping patterns [2]. One factor that makes studying droughts so problematic is that no single definition exists for drought [3]. This creeping phenomenon, as it has been called due to its slow onset, means different things to different water users. For a reservoir manager, a drought might occur when the water level in the reservoir drops below certain thresholds. For a meteorologist, it might be the departure of rainfall from the long-term average for a region. For a farmer, it might be the depletion of soil moisture such that it no longer supports the growth of crops. Droughts have been categorized into different types depending on which stage in the hydrometeorological cycle the effects are felt. Meteorological drought may be defined as a shortfall of precipitation as compared to the long-term average for that region. Agricultural, or soil moisture, drought is said to occur when the soil moisture depleted to an extent where it is not enough to support the healthy growth of crops and vegetation. Hydrological drought occurs typically over a longer period, when the water flows in streams and rivers drop below the long-term average. When drought causes adverse impacts on society, it is said to be a socio-economic drought [3]. Recently, groundwater drought is also being discussed as a new type of drought, which is identified by a shortage in groundwater. To monitor and study the propagation of droughs, researchers have developed various indices. [PERSON] et al. [4] employed the self-calibrated Palmer Drought Severity Index (PDSI) [5] to explore the characteristics of meteorological and hydrological droughs in South Africa. Focusing on the quantification of drought duration and severity, [PERSON] and [PERSON] [6] introduced the Effective Drought Index (EDI), which requires daily precipitation data. Numerous studies have made use of another popular drought index, the Standardized Precipitation Index (SPI) [7], to study the characteristics of droughs in various parts of the world [8; 9; 10; 11; 12]. An upgrade to SPI is the Standardized Precipitation Evapotranspiration Index (SPEI) introduced by [PERSON] et al. [13] in 2010. The calculation procedure is similar to that of SPI except that SPEI also uses potential evapotranspiration as an input, in addition to precipitation. Therefore, SPEI reflects the effects of temperature on droughs, and so is more suitable for drought monitoring in a changing climate. There have been various studies conducted that show the efficiency of SPEI as an index to monitor and characterize droughs [14; 15; 16; 17; 18; 19; 20; 21; 22]. SPEI has also been documented to be a suitable indicator for monitoring droughs in Pakistan [14; 23]. Pakistan has been ranked among the top 10 countries severely affected by the adverse impacts of climate change [24]. The main hazards in Pakistan are floods and droughs. Balochistan province is among the most vulnerable to droughs due to its arid climatology, high exposure, and low adaptiveness [25]. A study [10] used SPI to characterize droughs in Balochistan from 1975 to 2010. It concluded that more than 70% of the meteorological stations demonstrated negative trends in precipitation after applying the Mann-Kendall test. However, the period chosen for this study does not provide a complete picture of the evolution of droughs throughout the 20 th century. Furthermore, SPI does not reflect the changes in evaporative demand occurring due to warming.