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Drought Indices Monitoring using SPI and Z Index Score for Gua Musang, Kelantan

Drought has become prevalent in Malaysia due to exceptional rainfall deficit which in turn exacerbate the existing local water crisis. This paper is intended to determine the drought index in Gua Musang as one part of contribution to the development of drought index for the whole of Malaysia using the Standardized Precipitation Index (SPI) and Z score Index (ZI). The data collection used the rainfall data according to the identified station starting 2003-2015 based on the completeness of the data. The results indicated that the SPI and ZI gave quite similar result in term of condition of drought event and depicted the strong correlation between SPI and ZI. Findings from this study is believed benefit water engineers by providing information a probability distribution of water scarcity under different drought condition thus the mitigation strategy can be taken in order to address the impacts especially on water supply.


Introduction
Numerous human activities have led to global warming, which often came with high frequency of extreme events that are related to change in water circulation, such as drought and flood at the global scale (Leng et al., 2015). Recently, the scientist has predicted that the extreme drought event for three consecutive years starting on 2019 and the scientist have to come out with various investigations on the drought analysis and prediction such as spatial and temporal differences of drought, the mitigation of drought effects and drought prediction based on various atmospheric circulations indices (Lana et al., 2001;Huang and Chou, 2008;Cordery and McCall, 2000).
There are many methods to monitor drought that have been developed and applied over the past decade such as Standardized Precipitation Index (SPI), Standard Precipitation and Evapotranspiration Index (SPEI), Palmer Drought Severity Index (PDSI), Percent of Normal (PN), Z score , Surface Water Supply Index (SWSI) and Effective Drought Index (EDI) (Palmer, 1965 (Yusof et al., 2012). However due to the climate change problem recently, Malaysia also experienced with the drought through the series of drought event in 1992, 1998 and 2015. In 1998, the drought event was associated with El-Nino and gave a huge effect from Perlis (The northern state of Peninsular Malaysia), up to the state of Negeri Sembilan and Melaka and the worst hit the Kuala Lumpur and part of Selangor during that time where water rationing had to be exercised and as a result affecting around 3.2 millions of users for about 5 months as from April to September (Nur Adawiyah et al., 2014) and it was called as national water crisis. Since then, there were a movement on the drought study in Malaysia such as assessment of drought impacts on vegetation health, a case study in Kedah by combining two types of drought assessment which are meteorological part using Standard Precipitation Index (SPI) and the agricultural part using Normalized Differentiation Vegetation Index( NDVI) (Othman et al.,2016) , the usage the SWSI and SIAP software to determine occurrences of drought in Langat River Catchment (H. Khan et al., 2018) and trend analysis with respect to the drought episode according to the potential evapotranspiration based on temperature variable (Hui Mean et al., 2018). Therefore, there is an opportunity to develop drought indices which can be applied for early detection of droughts including their intensity and spatial extent. Thus, the intention of this paper is to determine the drought indices in order to contribute to the development of drought indices for the whole of Malaysia

Site Description
Kelantan is situated in northeast Peninsular Malaysia between latitudes 4° 40' to 6° 12' North and longitude 101° 20' to102° 20' East. Kelantan can be divided into several districts such as Pasir Mas, Kota Bharu, Bachok, Pasir Puteh, Machang, Tanah Merah, Tumpat, Jeli, Kuala Kerai and the largest district is Gua Musang. The annual precipitation over the area varies between 0 mm in the dry season from March to May and 1750 mm in the wet or monsoon season from November to January. Figure 1 shows the location of Kelantan and its districts. The rainfall data were collected based on selected station for area Gua Musang as shown in Table  2   Standardized Precipitation Index (SPI) was designed to identify the level of deficiency in rainfall on various time scales. It is based on the specified non exceedance probability of rainfall of certain time scale e.g weekly, monthly, yearly. In order to determine the non exceedance probability of rainfall, empirical or a theoretical, the probability distribution function is used. It generally used index among multiple drought indices to track the meteorological drought events where the less than or equal to -1 is categorized as drought spell (Palmer, 1965). The SPI can be expressed as;

SPI = (1)
Where x is the rainfall data, μy and σy are the mean and standard deviation of ln (x) respectively. Various drought categories are defined for different threshold values of negative SPI values e.g -3,-2.5,-1.5,-1,-0.5 and 0 are displayed in Table 3.   subjected to an upward trend throughout the dry season, particularly eastern and western regional. This trend analysis is important tool to extract an underlying pattern of behaviour and provides useful information on the possibility of tender of variation (Yue and Wang, 2004). Other study conducted by Yusof et al. (2013) indicated the finding that there is a possible of drought episode since it is shown that the high possibility of occurrence with respect to its duration and severity.    Figure 2. Correlation between SPI and Z indeks score method

Conclusion
Findings indicate the SPI and ZI are good tools to define, detect and monitor drought. The versatility of SPI and ZI allow for the monitoring of drought at the different time. Linear regression between ZI and SPI has a good correlation thus can be useful in monitoring and prediction of drought. Thus, it shows that study on the effects of drought is important to address the impacts especially on water supply.