What is the trend of climate change in a region? And what solutions are there to combat this trend of change?

Temperature and precipitation are the main components of the climate that affect human settlements. Global warming (GW) increases the risk of extreme weather events, such as heatwaves (HWs), dry spells (DSs) and flooding (FL). The IPCC [1] (p. 82) states, “It is virtually certain that the frequency and intensity of hot extremes and the intensity and duration of heatwaves have increased since 1950 and will further increase in the future even if global warming is stabilized at 1.5 ◦C. The frequency and intensity of heavy precipitation events have increased over a majority of those land regions with good observational coverage (high confidence) and will extremely likely increase over most land regions with additional global warming”.Summer HWs have increased in frequency and duration in most of the world since the 1960s [2,3]. Trends show that, in the future, with a warmer climate and increased mean temperatures, heatwaves will become more intense, longer lasting, and/or more frequent [4]. Hence, it is highly likely that climate change causes an increase in HWs, which negatively affect human health. The increase in extreme heat events, as a result of GW, seems to be accompanied by an increase in the variability of precipitation, with a progressive increase in periods of drought and extreme precipitation. Greater warming over land alters key water cycle characteristics. The rates of change in mean precipitation and runoff, and their variability, increase with global warming. “The frequency and intensity of heavy precipitation events have increased since the 1950s over most land area for which observational data are sufficient for trend analysis (high confidence) and human-induced climate change is likely the main driver. Human-induced climate change has contributed to increases in agricultural and ecological droughts in some regions due to increased land evapotranspiration (medium confidence)” [1] (p. 8). However, the variation in drought periods is much more uncertain. It affects certain regions, but not on a global scale [1]. Precipitation deficits and changes in evapotranspiration determine net water availability. A lack of sufficient soil moisture, sometimes amplified by an increased atmospheric evaporative demand, leads to agricultural and ecological droughts. A lack of runoff and surface water leads to hydrological droughts [5–9]. The Mediterranean region, and especially the Iberian Peninsula, are hotspots of the global warming (GW) process. . Over the past few decades, a substantial body of research has indicated that the rate of temperature increase in the region is significantly faster than the global average, with Spain being particularly prominent in this trend [10–15]. Studies based on observational data and climate models have revealed a significant rise in temperatures in the Mediterranean region from the second half of the twentieth century to the early twenty-first century. These results are aligned with predictions from global and regional climate models [1]. In addition, in the CMIP5 ensemble of global climate models, the Western Mediterranean region shows a notable warming trend, particularly during summer, which is closely correlated with an increase in extreme temperature events [13]. According to the results of the CMIP6 historical models, the average temperature in Spain between 1971 and 2022 has increased by 1.6 ◦C, which is slightly above the Mediterranean temperature rise (1.58 ◦C) and well above the world average (1.19 ◦C). The Mediterranean region, with a dense and aging population, is one of the world’s areas most affected by climate change due to the increasing frequency and intensity of heatwaves [16–21] and prolonged droughts [22,23]. Evidence suggests that both the frequency and intensity of heatwaves have risen across Spain and other European countries. An analysis of European heatwaves from 1971 to 2010 by Russo et al. [24] identified a marked increase in frequency in the Mediterranean, with Spain emerging as one of the most severely impacted countries [15,25–29]. In parallel, European countries, and Spain in particular, have experienced significant changes in precipitation patterns under the influence of climate change [30,31]. Projections suggest that the overall average annual precipitation in the Mediterranean region will decrease in the future, with increasing periods of drought, while the frequency and intensity of extreme precipitation events may also increase. This trend is particularly pronounced in areas close to the Mediterranean coast, where there has been a significant increase in periods of drought and intense rainfall [12,32]. The great variability in the rainfall regime in the Mediterranean region and in Spain is another widely studied research topic [33,34]. Despite these insights, much of the existing literature has primarily concentrated on changes in total precipitation. The interactions between different types of extreme precip-itation events are often overlooked. Additionally, there remains a gap in understanding the driving mechanisms behind shifts in precipitation patterns and the regional variability under diverse geographical conditions [35,36]. Amid the ongoing shifts driven by climate change, the link between temperature and precipitation changes has become more apparent, particularly during extreme events [37,38]. Studies have shown a strong negative correlation between rising temperatures, especially maximum temperatures, and reduced rainfall and increased droughts in the Mediterranean region and Spain [39,40]. Further analyses have deepened this understanding, revealing that extreme high temperatures are closely linked to reduced precipitation, whereas an increase in nighttime minimum temperatures is positively correlated with a rise in extreme precipitation events [32]. In summary, although there has been substantial research on climate change’s impact on Spain’s climate, several research gaps remain. First, most studies have concentrated on relatively short time frames and lack an in-depth analysis of climate change trends over longer timescales. Second, the complex interactions between temperature and precipitation changes, and the associations and driving factors of extreme events, have not been sufficiently explored. Lastly, the variability in responses to climate change across geographical and climatic regions requires further investigation [35,36]. To better understand and predict changes in climate patterns, climate classification systems are essential tools. Commonly used systems worldwide include the Köppen–Geiger climate classification, the Thornthwaite climate classification, the Papadakis climate classification, the Trewartha climate classification, and ASHRAE Climate Zones, among others. The Köppen–Geiger climate classification is one of the most widely used systems. Initially proposed by Wladimir Köppen in the late nineteenth century [41,42] and later refined [43], it classifies global climates based on monthly averages of temperature and precipitation. This system divides global climates into 5 major categories and 30 subcategories. It offers an effective way to describe macro-characteristics of climate zones and their potential shifts with climate change [44,45]. In recent years, updates to the Köppen classification maps have incorporated 32 climate models from CMIP5 and high-resolution climate datasets, to enhance the accuracy of predictions and classifications for present and future climate scenarios [46].These climate classification systems not only help researchers to categorize various climate types but also provide a foundation for predicting the impacts of climate change. The Köppen–Geiger system, in particular, remains a cornerstone in climate research due to its adaptability to various climate data and scenarios. This makes it highly effective for tasks such as global vegetation mapping, ecological modeling, and climate impact assessments [47,48]. Spain has applied several climate classification systems to study regional climate dynamics and their impacts. Using information from the years 1931–1960, Inocencio Font, a member of the Spanish National Institute of Meteorology (the predecessor of the current AEMET), developed in 1983 [49] a climate proposal for the Iberian Peninsula. This classification, which is based fundamentally on two factors, the continentality index and the rainfall regime, adapts quite precisely to the specificity of climates in Spain. However, it does not consider the significant climate change that has occurred since 1960. Another important contribution was made by Martín-Vide and Olcina Cantos [50]. In this study, the authors proposed a climate classification based mainly on physiographic criteria, according to precipitation and mean annual temperature, seasonal rainfall, and thermal amplitude, among other characteristics. In addition to these studies, scholars in Spain have employed other climate classification methods to understand various climatic and ecological aspects. The Papadakis climate classification, which focuses on bioclimatic zones defined by temperature and humidity, is particularly useful for agricultural and ecological studies. Recent research has used this method to assess the impacts of climate change on the suitability of various Mediterranean crops in Spain [51]. In order to evaluate the energy efficiency of buildings, the adaptation of the European Energy Performance of Buildings Directive [52] has been implemented through the Technical Building Code (TBC), which divides the territory into climate zones and evaluates buildings’ energy performance based on these zones [53]. The Technical Building Code (TBC) segments Spain according to climate seasons. Some authors [54] have critically discussed the TBC climate classification, and proposed an alternative that is better adapted to the warming experienced by Spain in recent decades. In assessments of building comfort and energy efficiency, the ASHRAE climate classification has also been widely used. Studies have shown that ASHRAE standards [55] are useful for assessing thermal comfort in mixed-mode and naturally ventilated buildings. However, the standards often need adaptations to account for the Mediterranean climate. Optimizations of ASHRAE standards through adaptive comfort models have been proposed to better fit Spanish climates. These can be used to improve energy simulations and optimize HVAC systems, to enhance building performance and occupant comfort [56,57]. However, among all the studies that analyze the climate in Spain, the Köppen–Geiger classification is undoubtedly the most commonly used. This classification has been widely applied to study regional climate changes and predict future trends. The State Meteorological Agency (AEMET) has provided an extensive analysis of the changes in Köppen climate types in Spain from 1951 to 2020 [58]. Building on these climate classification systems and understanding the dynamics of temperature and precipitation changes in the Mediterranean region, particularly in Spain, are crucial for assessing the impacts of climate change [59,60].

Climate is the prevailing weather conditions over a long period of time. In fact, the climate of a region is made up of a set of elements and factors that result from the changes in each element due to climatic factors. This creates special conditions in terms of weather that are unique for each region (Doulabian et al., 2021). Although the flow regime shows seasonal variations in river flow, it does not provide accurate information on the magnitude and frequency of floods and droughts. The study of flood behavior is very important because they are able to carry significant amounts of sediment and play an influential role in canal formation. Climate change has led to changes in the worldwide hydrological regime in recent decades, so that the likelihood of exposure to maximum climatic events such as floods has increased. Since increasing this probability for future periods could have detrimental effects on human societies, in recent years, research on this issue has been considered for various catchments around the world (HassanMohammed et al., 2021; Eslaminezhad et al., 2022). Hydrological hazards occur as a result of changes in the frequency and intensity of rainfall, rising temperatures and changes in land use. Global warming has led to increasing rainfall and decreasing snowfall in winter, rising the river levels and increasing river discharges. This increase causes life and property losses and increases the likelihood of flooding. Therefore, by examining the factors affecting the change in flood intensity and appropriate management practices such as the development of watershed management, forestry, etc., the volume of flood damage can be reduced in the basin. Changes in climatic parameters such as precipitation affect the river flow regime. Given the impact of climate change on human life, an effort to understand more about climate change events is essential. The metropolis of Mashhad has a wide geographical location in the alluvial plain. Being located between the sedimentary heights of Kopehdagh and Hezarmasjed has led to the creation of a special morphology for the alluvial plain of Mashhad. The Kashafrood River drains all the rivers of Mashhad plain and the drainage rivers of the Binalood heights pass through Mashhad city and discharge into the Kashafrood River. The physical development of the city over the years has led to changes in the morphology of the city’s rivers, and in some areas on the riverbeds, high-rise structures have been built with high importance and have increased the likelihood of hazards (Azamizade et al., 2021).The structures that have been created due to the beautiful landscape in the highlands of the metropolis of Mashhad are built exactly on waterways. As a result of the reduction in water infiltration, the runoff volume created is generally high, which in turn increases the likelihood of flooding and its severity in residential and commercial areas. These issues make the city vulnerable to increases periodic floods (Eslaminezhad et al., 2020). Ghorbani (2002) used 40 years of meteorological statistics at Gorgan Station to study climate change. The rate of change in temperature and precipitation was investigated by the simple linear regression method. According to the results, no significant changes in temperature were observed but rainfall decreased. In our country Azizi et al. (2004) studied the presence or absence of temperature and precipitation trends. Asgari et al. (2006) studied the trend of eleven precipitation indices across the country and found that in about two-thirds of countries, the annual precipitation index had a negative and positive trend in wet days and heavy rainfall days, respectively. Hosseinzadeh et al. (2007) investigated the issue of floods and flooding in Mashhad and expressed the indirect effects of urban expansion within catchment areas and the possibility of flood intensification in the urban context. Avand et al. (2011) Investigated the effects of climate change and land use on flood prone areas in the Tajan watershed of Iran. The results showed that elevation (21.55), distance from the river (15.28), land use (11.1), slope (10.58), and rainfall (6.8) are the most important factors affecting flooding in this basin. The factors were modified according to land use changes and climate changes and the models were revised. Landuse and climate forecasting in this region indicate that land use change, like decreased forest cover (−77.19 km2 ) and reduced rangeland (−218.83 km2 ) near rivers and downstream, can be expected and rainfall is projected to increase (under both scenarios). These changes would result in increased probabilities of flooding in the downstream portion of the watershed and near the sea. Darand et al. (2013) investigated the temperature and precipitation behavior at Kermanshah station. The results showed that cold extreme indices in Kermanshah are decreasing while extreme warm indices are increasing. Sayemuzzaman et al. (2014) examined the trend of seasonal and annual rainfall in North Carolina, USA. In order to analyze the annual and seasonal temporal and spatial trends, they used the Mann- Kendall test for uniform distribution of 249 precipitation data in North Carolina during the statistical period (1950–2009), respectively, to determine its trend and significance. The local trend of precipitation (mountainous, foothills and coastal) was also determined by the tests mentioned above. Before using statistical test, pre-bleaching method was used to eliminate the correlation effect of precipitation data series. The results show a significant increasing and decreasing trend in winter and autumn rainfall, respectively. For annual, spring and summer rainfall, a combined (increasing/decreasing) trend has been identified. Significant trends were detected in only 8, 7, 4 and 10 stations out of 249 stations in winter, spring, summer and autumn, respectively. The amount of annual precipitation varies between 5.5 to 9 mm per year. In spatial trend analysis, increased precipitation has been recorded in mountainous and coastal areas throughout the period except in winter. In the foothills area, the trend is rising in the summer and autumn, but decreasing in the winter and spring. Modarres et al. (2016( studied the great changes in the flood and the severity of drought in Iran for the years 1950 to 2010, with changes in the time interval in some stations. Both increasing and decreasing trends were observed for drought severity and flood magnitude in different climate regions and major basins of Iran using these tests. The increase in flood magnitude and drought severity can be attributed partly to land use changes, an annual rainfall negative trend, a maximum rainfall increasing trend, and inappropriate water resources management policies.Waikar (2014) has calculated that the rate of water discharge in a drainage basin has an inverse relationship with drainage density. In this case, factors such as walling the banks of floodways and removing the mazes change the characteristics and morphology of the river. Ahmad et al. (2015) investigated the precipitation changes at 15 stations in Pakistan’s Swat River basin over a 51- year period (1961-2011). They used nonparametric Mann-Kendall and Spearman statistical tests to detect monthly, seasonal, and annual precipitation trends. The results of monthly, seasonal, and annual precipitation show a combination of positive (incremental) and negative (detractive) trends. One station in particular, Sayed Sharif station, recorded the most significant monthly rainfall. On a seasonal time scale, the precipitation trend has changed from summer to autumn.Sayed Sharif station showed the highest positive trend (7.48 mm/year) in annual precipitation. Across the Swat River basin, a statistically significant trend was found for the annual rainfall series. The lower Swat basin, however, showed the maximum increase in precipitation (2.18 mm/year). Also, the performance of MannKendall and Spearman tests was constant at the significantly confirmed level. Zhou et al. (2019) examined the effects of recent urban development on hydrological runoff and urban flood volume in a large city in northern China, and compare the effects of urbanization with the effects of climate change under two representative focus paths (RCPs 2.6 and 8.5). They then map the urban drainage system to reduce flood volume for future adaptation strategies. The results show that urbanization has led to an annual increase in surface runoff of 208 to 413%, However, changes in urban flood volume can vary greatly depending on the performance of the drainage system during development. In particular, urbanization changes in the expected annual flood volume range from 194 to 942 percent, which is much greater than the effects of climate change under the RCP 2.6 scenario (64 to 200 percent). Sun et al. (2021) examined an urban rainstorm model and a scenario simulation method in downtown Shanghai. First, the flood risks in the study area under the influence of future climate change were investigated using a simulation with different rainfall return periods. They then evaluated the benefits of traditional drainage system adaptation measures and low-impact development (LID) practices in reducing urban flood risks. The results show that the volume of urban floods increases non-linearly with increasing rainfall intensity under climate change. The maximum flood zone increases accordingly and is much more sensitive to smaller rainfall events. Both traditional drainage adaptation measures and LID practices can effectively reduce floods. Pal et al. (2022) explore future floods in India due to climate change and land use. Human activities and related carbon emissions are a major cause of land use and climate change, which has a significant impact on floods. They provide flood sensitivity maps for various future periods (up to 2100) using a combination of remote sensing data and GIS modeling. To quantify future flood susceptibility to various flooding factors, the Global Circulation Model (GCM) of precipitation and land use and land cover (LULC) data are predicted. They evaluated the current flood sensitivity model through the receiver performance characteristic curve (ROC), in which the area under the curve (AUC) shows 91.57% accuracy of this flood sensitivity model and can be used to model future flood sensitivity. Based on the predicted LULC, rainfall and flood sensitivity, the results of the study indicate that the maximum monthly rainfall in 2100 will increase by approximately 40 to 50 mm, while the conversion of natural vegetation into agricultural land and is about 0.071 million m2 and the area of severe flooding will now increase to 122% (0.15 million km2 ).A flood is considered as one of the Natural disasters and the limiting factor of development, especially along coastlines and river banks. Therefore, studies of flooding and flood prevention are important in water resources management. It is beneficial to identify flood-prone areas in watersheds when planning infrastructure programs for rural, agricultural and industrial development. Due to the fact that the Kashafrud watershed has critical and supercritical flood potential in some areas, especially in Mashhad and Chenaran, the importance of studying changes in the intensity and duration of floods increases. Kashafrud river basin is a part of Qaraqoom catchment in Iran. This catchment is located in the northeast of thecountry and in the north of Khorasan Razavi province. It has an area of 15,650 km2 . In the Kashfrud watershed, several authors conducted studies on flooding. BaniWaheb et al. (2006) investigated regional flooding in the Western Kashafrud river basin. The results showed that among the factors affecting the flood, the average of maximum 24-h precipitation and the percentage of area covered by vegetation had a more significant effect on the maximum instantaneous discharge values than other factors. Barati et al. (2011) analyzed the regional flood frequency in the Kashafrud catchment using the linear moment method. Based on the linear moment diagram and the Zdist statistic, the distribution of generalized limit values has been identified as an appropriate distribution for the study area. Sayari et al. (2011) compared two models of general atmospheric circulation in predicting climatic parameters and water needs of plants under climate change in the Kashafrud River basin. The results showed that the average annual rainfall with the model (CGCM2) and two scenarios (A2, B2) decreased by 13 and 16%, respectively. But for the model (HADCM3), the average annual rainfall was increased by 2 and 8%. The model (CCCM2) and two scenarios (A2 and B2) decreased by 13 and 16 percent. Azamizadeh et al. (2019) investigated the flooding potential of Kashafrud river basin of Mashhad by SCS method in CIS environment. The results showed that 68.25% of total basin area has normal flood potential, 25.5% is critical, 6.25% has supercritical flood potential. Helmi and Shahidi investigated the impact of drought on the water quality of Kashfroud river using precipitation, temperature, and quality data from six stations over a 30-year period. They found that during drought, water quality parameters such as TDS, EC, Ca, Mg, Na, SO4-, HCO3-, and Cl- increased significantly compared to the long-term average. The concentration of Cl- reached a maximum of 7.66 mg/l at Olang Asadi station. Additionally, the increase in temperature during drought led to the highest water quality changes at Olang Asadi station. Overall, the study concludes that drought, coupled with reduced rainfall and increased temperature, results in decreased water quality, particularly downstream. The purpose of this study was to examine the statistical trend of monthly and annual series, flood discharges of the Kashafrud river basin. Therefore, statistical data of the last 65 years related to the monthly and annual series of the station were examined using Excel and SPSS software.