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IntroductionClimate change and human interventions are the most important factors that in combination influence the hydrological response of a watershed system. In order to increase the level of their social and economic welfare, human beings have made serious and significant interventions in nature and directly caused several changes in its functions and processes, particularly the hydrological cycle. On the other hand, global climate change imposes several impacts on the natural hydrological cycle. Therefore, the separation of the effects of direct human intervention and climate change on the hydrological processes is of great importance for land use planning, water resources management, and socio-economic development policy-making. The hydrological cycle is one of the most important natural processes subjected to human interventions and climate change, whereas its various aspects and components get altered. One of these hydrological components is the river flow discharge, which is jointly affected by climate change and human interventions, and it will have dire consequences on different aspects of human life. Human activities indirectly (through the emission of greenhouse gases) and directly (through activities such as the construction of dams, water diversion structures, water consumption for agricultural activities, and land use change) affect the hydrological cycle and the natural regime of river flows. Materials and MethodsThe area studied in this research includes the upstream part of the Hablehroud watershed draining to the Bonekouh hydrometry station. The whole study area is located within the administrative boundaries of Tehran province. Hablehroud River, which is the main drain of the watershed, has been under pressure in recent years as a result of human activities and climate changes, and its hydrological status has altered significantly during past decades attracting the attention of watershed inhabitants and local authorities mostly blame the climate change as the main cause of the hydrologic alteration. The current research is conducted in order to determine the contribution of climate change and direct human interventions on the discharge decline of the Hableroud watershed. In this research, the hydrological sensitivity analysis approach based on the Budyko hypothesis was used in order to separate the effect of climate change and direct human interventions in reducing the discharge of Habaleroud River at the location of Simindasht and Delichai hydrometric stations. The annual time series of flow discharge during the period 1981 to 2017 was used. Two solution methods by Fu and Zhang have been used to solve the Budyko equation. Prior to the calculation of the contributions, the significant change point along the time series was detected by three tests of the Buishand Range, Standard Normal Homogeneity, and the sequential Mann-Kendall. Results and DiscussionDespite an infinitesimal variation, all the change point detection tests showed that a significant change point occurred in the middle of the 1990s for the annual discharge time series of the both hydrometry stations of Delichai and Simindasht. The contribution of climate change on discharge in the Simindasht and Delichai hydrometry stations was, respectively, calculated as less than one and 53 % according to Fu's method and -6 and 93 % according to Zhang's method. According to Fu's method, the contribution of human intervention in the discharge change of Simindasht and Delichai stations has, respectively, been calculated as -81 and -153 %, and according to Zhang's method as -94 and -193 %. The positive percentage values indicate the incremental effect on the flow discharge and the negative values indicate the subtractive or lessening effect. The results indicated that although the absolute and percentage values of the contributions calculated by both solution methods of the Budyko equation vary somehow, the direction (positive and negative effects) and the relative magnitude of contributions of the human interventions and climate change are similar for two solution methods of the Budyko equation. As can be noticed, at both the studied hydrometry stations, the effect of human intervention is much higher than the climate change effect. Another important point is that the effect of climate change on the flow discharge is subtractive only at the Simindasht hydrometry station according to Zhang’s method, and is incremental for other cases. In other words, climate change has resulted in increasing inflow discharge across the study area. Furthermore, the results of the study indicate that the effect of direct human interventions on the flow discharge is more intensive across the Delichai sub-watershed. ConclusionsAccording to the results of the study, it can be concluded that the main factor in the reduction of discharge in the Habaleroud River is direct human interventions and climate change has a very small contribution to it. Due to the fact that land use change is the main indicator of human interventions done in line with the main policies and strategies, developing proper policies and strategies to prevent inappropriate land use changes is necessary. Therefore, it is suggested that local policymakers and water resources managers develop and enact policies in order to manage the human activities influencing the natural water cycle. Furthermore, the results of this study can be used as a reference for the development, exploitation, and management of water resources in the future. |
