Document Type : Research Article
Authors
1
Yazd University Department of meteorology and climatology.
2
Department of Geography, Yazd University
3
Associate professor in Climatalogy , Department of Geography, Yazd University
Abstract
One of the most contentious issues among contemporary climatologists is the existence of climate change and alteration in the trends of atmospheric parameters. The primary aim of this research was to examine the trends in precipitation and temperature changes under climate change conditions, and to predict future temperature and precipitation in the Kabul Drainage Basin, Afghanistan. To evaluate the impact of climate change on precipitation and temperature parameters, detection, trend analysis, prediction, and model accuracy analyses were conducted. In this process, methods such as anomalies, the non-parametric Mann-Kendall test, Theil-Sen's slope, the LARS-WG model (sixth report), and statistical indices such as the correlation coefficient, coefficient of determination (r, R²), RMSE, and NRMSE were used. The research findings indicate that in the Kabul Drainage Basin, the trends in these parameters are positive, with increasing annual average precipitation and increasing annual average temperature. The rainy season has gradually shifted from winter to summer. Specifically, the annual precipitation between 1979 and 2020 increased by approximately 0.30% or 0.93 mm, while the temperature increased significantly by about 8% (1.2°C). Predictions suggest that the trend of increasing temperature and decreasing precipitation will continue from the baseline period (1991–2021) into the 2021–2050 period. Across all scenarios SSP1-2.6, SSP2-4.5, and SSP5-8.5 the minimum temperature is projected to increase by 0.4°C, 0.5°C, and 0.6°C, respectively, and the maximum temperature by 0.6°C, 0.7°C, and 0.8°C compared to the baseline period. Annual precipitation is also expected to decrease by approximately 11% compared to the baseline period. Therefore, the impacts of climate change, including increased temperatures and altered precipitation patterns, are likely to exacerbate the risk of floods and related hazards in the future. The study of precipitation and temperature parameters under climate change is crucial. Accordingly, adaptation strategies for climate change and the enhancement of resilience are recommended.
Extended Abstract
Introduction
Climate change, as one of the most critical challenges of the present century, has had widespread effects on the environment, water resources, agriculture, and human livelihoods worldwide. It remains one of the most controversial topics in climatology. Most climatologists believe that changes in temperature or precipitation cannot simply be interpreted as long-term or short-term climatic fluctuations. Studies indicate that climate change is a global threat that disrupts the sustainability of various components of the Earth's system. Therefore, understanding current conditions and making climate projections are essential for identifying vulnerabilities and developing strategies to adapt to climate change.
Long-standing internal conflicts, diverse climates, complex topography, and a lack of meteorological stations have hindered extensive research in this field. To date, no comprehensive scientific studies have been conducted on precipitation and temperature trends in the Kabul Basin. While numerous global studies exist, research efforts in Afghanistan have been limited. Among the few studies in Afghanistan are those by Babar et al. (2016), Aliyar, Dhungana, and Shrestha (2022), Broomand (2015), Mestarshed (2013, 2014), Nasrati (2018), Sharafat (2020), and Salehi (2022). These studies indicate a declining trend in precipitation, particularly during spring and winter, and a rising trend in temperature across Afghanistan.
The Kabul River Basin, due to its unique geographical location and climatic conditions, has been significantly impacted by climate change, experiencing notable alterations in precipitation and temperature parameters. This region not only holds critical importance for water supply and agriculture for its inhabitants, but also warrants closer examination due to the frequent occurrence of floods and droughts. A detailed assessment of precipitation and temperature trends in the basin is essential.
The primary objective of this study is to investigate the impacts of climate change on precipitation and temperature variables and to forecast these parameters in the Kabul River Basin. This research employs various methods, including anomaly detection, the non-parametric Mann-Kendall test, Sen’s slope estimator, the LARS-WG model, and correlation coefficients, to analyze precipitation and temperature trends and address the existing research gap.
Material and Methods
This study utilized ground-based data from 28 meteorological stations over the period 1979–2020, as well as atmospheric data from NASA's MERRA-2 dataset. In 2021, missing precipitation and temperature data for the years 1979–2020 were completed by Japanese researchers using the gap-filling method. Due to the lack of daily ground-based precipitation and temperature data, daily precipitation and temperature records for 1991–2020 were downloaded from NASA's MERRA-2 platform. Missing and anomalous data were completed using statistical methods such as moving averages, and outliers were identified and removed using statistical tests like the Shapiro-Wilk test.
Analytical methods, including anomalies, the non-parametric Mann-Kendall test, Sen's slope estimator, and statistical indices such as the correlation coefficient (r), coefficient of determination (R²), RMSE, and NRMSE, were applied in the analysis. Trend analysis was conducted using the anomaly method (Equation 1) and the Mann-Kendall test (Equation 2). Using outputs from the Sixth Assessment Report of the IPCC and the LARS-WG8 model (HadGEM3-GC31-LL-CMIP6), climatic elements were projected for the 2021–2050 period. The validation of the results was conducted using statistical measures, including r, R², RMSE, and NRMSE (Equations 4, 5, and 6). Data analysis was performed using ArcGIS, Excel, and SPSS software.
Additionally, using validation indices such as the correlation coefficient (r), root mean square error (RMSE), and normalized root mean square error (NRMSE), along with observational precipitation and temperature data from five meteorological stations in the Kabul River Basin for the period 1991–2020, the outputs of the LARS-WG8 model were validated. The results confirm the satisfactory performance of the model in generating downscaled precipitation and temperature data.
Results and Discussion
The Mann-Kendall test, recommended by the World Meteorological Organization, was used in this study to analyze the annual rainfall trend. This statistical method is a standard approach for evaluating temporal trends in hydrological data. The results, presented in Table 2, indicate that during the period 1979–2020, the mean annual rainfall was 310 mm, with minimum and maximum values of 116 mm and 358 mm, respectively. Using a 95% confidence level (α = 0.05), the calculated Z-statistic for the Mann-Kendall test was 1.96, confirming a statistically significant increasing trend. An annual rainfall increase of 0.30% was observed in the Kabul River Basin.
Similarly, the trends in annual minimum, maximum, and mean temperatures were analyzed, as detailed in Table 3. The results reveal significant increases in all three temperature parameters. Specifically, the Mann-Kendall test showed that the annual minimum temperature exhibited the most pronounced trend, with a Z-value of 5.25, followed by significant increases in the annual mean and maximum temperatures. Analysis of the data in Table 2 confirms that all temperature types have risen considerably over the period 1979–2020.
Figure 5, based on Table 2, illustrates the temporal trend of annual mean temperature in the Kabul River Basin, highlighting a clear and substantial increase over the study period. These findings, combined with the lack of effective adaptation measures to address climate change, suggest that the observed trends are likely to continue. This ongoing temperature rise is expected to accelerate glacier melting, leading to a higher frequency of floods in the basin in the coming years.
Conclusion
The results of this study indicate that the annual precipitation in the Kabul Basin during the period 1979–2020 experienced an insignificant increase of approximately 0.3%, equivalent to 0.93 mm, while temperature exhibited a significant rise of nearly 8%, corresponding to an increase of 1.2°C. Projections suggest that the upward trend in temperature and the downward trend in precipitation will persist during 2021–2050 compared to the baseline period (1991–2021). Under all Shared Socioeconomic Pathway (SSP) scenarios—SSP1-2.6, SSP2-4.5, and SSP5-8.5—minimum temperatures are projected to increase by 0.4°C, 0.5°C, and 0.6°C, respectively, and maximum temperatures by 0.6°C, 0.7°C, and 0.8°C, respectively, compared to the baseline period. Additionally, annual precipitation is expected to decrease by approximately 11% relative to the baseline. The forecasts further suggest changes in the region’s precipitation regime, specifically a reduction in the proportion of precipitation occurring during colder months compared to other months. Consequently, the ratio of solid precipitation (snow) to liquid precipitation (rain) is projected to decline in the coming years.
Keywords
Main Subjects
)
Send comment about this article