Analyzing and prediction of rainfall trends over Baghdad city

Rainfall is a key part of the hydrological cycle and alteration of its pattern directly affects the water resources. The changing pattern of rainfall in consequence of climate change is now concerning issues to water resource managers and hydrologists. The present study aims to analyze the trend and forecast annual rainfall in Baghdad. rainfall data for the period of 1979-2019 was analyzed in this study, Statistical trend analysis techniques namely linear and Exponential trend were used to examine and analyze the problem. The result shows that rainfall will decrease in both methods but the liner method gives a higher value. from plotting time series of annual rainfall see that very variation so 5- moving average made to reduce the variance of rain but still variations so second 5- moving average made give less variance for rain then teak liner trend the result show also trend will decrease but reach 125 mm less than liner trend of actual series.


Introduction
Rain is important climate elements where all world give it special attention for being the basis without which no kind of life in the world can be there. Climate changes have made the amounts of rain change, as some areas have heavy rain, while other areas receive little rain, and sometimes meteorological drought occurs (Abdul-Jabbar& Abdulkareem, 2021) Iraq climate divided to Semi-humid zone in the far north, Semi-dry zone and Dry zone in the middle and south of Iraq (A. G. Mutar etal.,2016).However, this does not mean that the central and southern regions of Iraq do not receive heavy rains. Rather, they receive rains of up to 89 mm per day, and in the southern and southeastern regions are exposed to torrential rains sometimes (

STUDY AREA
The study area is Baghdad city the capital of Iraq, located between latitude (33.452oN and 33.184oN) and longitude (44.189oE and 44.576oE) see Figure 1. The Tigris River passes through the city dividing it into two parts: Karkh (Western part) and Rusafa (Eastern part). Two methods of trend taken in this study liner trend, as show in gure.3 and exponential trend in gure.4, the trend( red line) in both methods is decrease with time. MAPT and MAD in exponential lees than in liner because that's mean the accuracy of exponential is the best .also MSD in exponential higher than liner Because outliers have an effect on it. The forecast of annual rainfall for next four years after 2018 made (green line) where in 2022 the amounts of it will be (150 mm ) in liner method but will be (125 mm) in exponential method.

Results And Discussion
The Simple Moving Average (SMA) method was discovered by G. U. Yule in 1909. The process of computing moving averages smoothens out the uctuations in the time series data. It 7 can be shown that if the trend is linear and the oscillatory variations are regular (Rahardja, D. ,2020). the average of a span of series values surrounding and including the current value. The span is the number of series values used to compute the average. If the span is even, the moving average is computed by averaging each pair of uncensored means. The number of cases with the system-missing value at the beginning and at the end of the series for a span of n is equal to n/2 for even span values and (n-1)/2 for odd span values. (Koutrasetal.,2020).
The 5 moving average (red line) in gure 5 show that rain still variation so we take second 5 moving average to know the liner trend (red line) as show in gure 6. the trend shows that rainfall decrease and in 2020 will be (138 mm)

Conclusions
The behavior of annual rainfall in Baghdad varies greatly, and it is di cult to determine its trend directly, so using the moving average method is a good but it is better to take the second moving average to give a higher accuracy in determining the trend.By compare between methods used in this study the resulted show that all trend of anuual rainfall will decrease next 4 years to reach more than (125 mm).
Abbreviations CMB Core-mantle boundary GOSAT Greenhouse Gases Observing Satellite JAXA Japan Aerospace eXploration Agency TRMM Tropical rainfall measuring mission Declarations Availability of data and material Data sharing not applicable to this article as no datasets were generated or analysed during the current study. Please contact author for data requests.

Competing interests
The authors declare that they have no competing interest.

Funding no funding
Authors' contributions IK proposed the topic, conceived the study. AK analyzed the data and helped in their interpretation. All authors read and approved the nal manuscript. The geographical location of the study area.