Quantifying the impacts of anthropogenic changes and climate variability on runoff changes in central plateau of Iran using nine methods

https://doi.org/10.1016/j.jhydrol.2021.127045Get rights and content

Highlights

  • Nine methods were used to investigate anthropogenic changes and climate variability.

  • Runoff changes in two selected areas were investigated.

  • Climate variability played a key role in runoff decline in the Ghaleh-Shahrokh watershed.

  • Anthropogenic changes had a major role in runoff decline in the Javanmardi watershed.

  • Each method has its advantages and disadvantages.

Abstract

Quantification of affecting factors on river regime changes can be greatly helpful for water resources planning and management in the basin. Both anthropogenic changes and climate variability have affected rivers’ regime and led to considerable social and economic impacts. Observations in most parts of the world indicate that the hydrological cycle has been influenced by human activity besides of climate variability. In this study, 9 different methods which are divided into three general categories have been used to determine the impact of anthropogenic changes and climate variability on runoff changes in two watersheds in the central plateau of Iran, including Ghaleh-Shahrokh and Javanmardi watersheds. The results indicate that climate variability plays a dominant role in runoff decline in the Ghaleh-Shahrokh watershed, accounting for 60.2% of the total decrease, while human activities accounted for 39.8 %. In the Javanmardi watershed, anthropogenic changes played a dominant role in runoff decline, accounting for 77.1% (on average). In comparison, 22.9% (on average) of the decrease was attributable to climate variability. Sensitivity analysis of the annual mean runoff shows that precipitation plays a key role in runoff changes in both study areas. After precipitation, changes in potential evapotranspiration and temperature have the greatest impact on the annual mean runoff in the studied watersheds, respectively. Comparison of the different applied methods indicate that elasticity-based methods are the fastest and intuitive methods to investigate the impacts of anthropogenic changes and climate variability on runoff changes. Despite this, using different methods should be taken into account.

Introduction

Both climate variability and anthropogenic changes have affected hydrological cycle according to the observational evidence from a number of basins in four corners of the world (Huntington, 2006). Climate variability has affected the variability of meteorological factors, especially precipitation and temperature (Eslamian, 2014, Nazari Tahroudi et al., 2019) and has increased the frequency of extreme value events (Rani and Sreekesh, 2018). Variability may be due to natural internal processes within the climate system (internal variability), or to variations in natural or anthropogenic external factors (external variability). The difference between climate variability and climate change goes back to a period of time. So that climate variability considers changes that occur within smaller timeframes. The global mean surface temperature increased by 0.87 °C from 2006 to 2015 in comparison with the historical average over the period 1850 – 1900 and it is projected to increase 1.5 °C between 2030 and 2052 if temperature continues to rise at the current rate (IPCC, 2018). Runoff in the basin is influenced directly and indirectly by changes in meteorological factors (Dam, 2003, Tabatabaei et al., 2020). On the other hand, the effect of anthropogenic changes such as urbanization, deforestation, desertification, dam construction, and reservoir operation on different elements of hydrological regime and water resources is taken for granted (Haghighi et al., 2014, Milly et al., 2005, Rahnama and Mirabbasi, 2010, Sharifi et al., 2021). Around the globe, especially in arid and semi-arid regions, declining runoff can lead to critical social and ecological issues (Fazel et al., 2017, Haghighi and Kløve, 2017). Water resources in these regions are more vulnerable to the adverse effects of climate change than other regions (Torabi Haghighi et al., 2020b, Zamani et al., 2017). Furthermore, per capita water availability is declining in these areas due to population growth and water-dependent economic development as the manifestations of anthropogenic changes (UN-Water, 2008). In this regard, determining the contribution of each of the factors of climate variability and human activities can provide useful information for managers and planners to design appropriate strategies to adapt to the runoff regime changes and reduce its adverse effects.

Runoff plays a crucial role in meeting environmental and human demands especially in hot seasons. Investigation of runoff changes in a basin not only reflects the characteristics of the river system, but also indicates the structural and environmental changes in the basin (Sharifi et al., 2017, Yao et al., 2015). Human activities affect runoff directly (e.g. land use change) and indirectly (e.g. increased greenhouse gas emissions). Assessment and quantification of anthropogenic changes and climate variability effects on runoff are crucial for water resources management in a basin. Addressing the impact of anthropogenic changes and climate variability on runoff changes separately can be contributed to the improvement, development and modification of measures planned for adaptation to climate change (Torabi Haghighi et al., 2020a, Wang, 2014).

In recent years, numerous studies have been done to investigate the relative contribution of human activities and climate variability impacts on long-term average change in runoff (Bao et al., 2019, Zeng et al., 2015, Zhao et al., 2015). The methods for separating anthropogenic change and climate variability impact on runoff can be divided into three groups, including empirical methods (Gao et al., 2011, Zhang et al., 2011, Zhao et al., 2014), elasticity-based methods (Gao et al., 2016, Wu et al., 2017, Ye et al., 2013), and hydrological modeling (Renner et al., 2012, Tomer and Schilling, 2009, Zeng et al., 2015, Zuo et al., 2014). Simple linear regression and double mass curve methods are the most common empirical methods. Gao et al. (2011) applied the double mass curve method to investigate streamflow changes in the middle reach in Yellow River during 1985–2008. They reported that human activities played a major role in streamflow reduction by 72%, which was much stronger than the precipitation contribution rate by 28%. Zhao et al. (2015), using simple linear regression, attributed that 72% of runoff decrease in the Yangtze River between 1953 and 2010 was due to climate change.

Nonparametric methods and analytical methods based on the Budyko hypothesis are the most common elasticity based methods that are broadly utilized to determine the relative contribution of human activities and climate change on runoff changes. Mwangi et al. (2016) used Budyko hypotheses to separate the respective contribution of drivers to change in runoff in the upper catchment of Mara River basin in Kenya. They found that land use change as the manifestation of human activities in the catchment was the main driver of change in runoff accounting for 97.5% of the change. Wu et al. (2017) used elasticity-based methods and Budyko hypothesis to investigate the hydrological response to climate change and human activities in the Yanhe River basin, as one of the Yellow River’s sub basins China from 1972 to 2011. They reported that climate change played a key role in decreasing runoff in the basin, with a rate of 54.1% of the total decrease in runoff. They also attributed 45.9% of the reduction of runoff to the effects of human activities.

Various hydrological models have been developed during the last decades to simulate runoff and hydrological cycle in a basin (Ren et al., 2020, Sharifi et al., 2017). The impacts of climate variability on runoff changes can be evaluated by comparing simulations driven by different climate variables in different periods (Wu et al., 2017, Zeng et al., 2015, Zuo et al., 2014). Kakaei Lafdani et al. (2020) applied Hydrologiska Byråns Vattenbalansavdelning (HBV) model to quantify different types of natural and human droughts in the Kiakola and Eskandari catchments in Iran. They reported that although both catchments have different climate conditions, human activities had a negative impact on the hydrological system and played a major role in longer and more severe drought.

Investigating most studies on the impact of human activities and climate variability on runoff change shows that most of them use a single method or appliy different methods in the same catchment. Generally, using different methods in the same study area often has a significant degree of uncertainty. To increase confidence, multiple methods have been applied to assess the relative contribution of human activities and climate variability on runoff changes (Liang et al., 2015, Wu et al., 2017, Zhao et al., 2015). There is an inconsistency in the obtained results using multiple methods because of variable complex effects of human activity and climate variability on runoff changes and geographical condition. Therefore, it is essential to have an in-depth and meticulous understanding and insight into the study area to determine the effects of human activity and climate variability on runoff changes.

Runoff sensitivity to climate variables can be evaluated by two main approaches, including hydrological models that apply different climate scenarios and elasticity-based models that use long-term observed data (Bao et al., 2019). The hydrological models approach has been applied broadly worldwide (Arnell and Lloyd-Hughes, 2014, Lopez et al., 2012, Montanari et al., 2013, Renner et al., 2012, Siam and Eltahir, 2017, Geshnigani et al., 2021). Recently, some researchers applied elasticity-based models and Budyko hypotheses (Budyko, 1974) to investigate the runoff sensitivity to climate variables. Hasan et al., (2018) used the Budyko framework in the Nile River Basin. They reported that a 10% decrease in precipitation results in a decrease in runoff from 19% to 30% in tropical and arid zones, respectively. In comparison, a 10% increase in precipitation leads to an increase in the runoff between 14% and 22% in tropical and arid zones, respectively. The impacts of the potential evapotranspiration formula are greater for wet regions than for dry regions (Kingston et al., 2009, Sheffield et al., 2012, Sperna Weiland et al., 2012); therefore, its impacts should be taken into account. Dakhlaoui et al. (2020) reported that runoff in semi-arid areas like Northern Tunisia is not sensitive to potential evapotranspiration estimates, but precipitation is the most sensitive climate variable in the study area.

In this study, we used nine methods that have been classified into three groups and applied them in two watersheds in the central plateau of Iran, including Ghaleh-Shahrokh and Javanmardi watersheds. This approach enables us to discuss the advantages, disadvantages and characteristics of all the methods. Therefore, the novel aspects of this study are as follows: (1) to review the nine different methods in all its aspect and explain the respective merits, demerits and limitations, (2) to apply and compare the performance of the different methods in the selected watersheds and determine the relative contribution of anthropogenic changes and climate variability on runoff changes, and (3) to characterize the sensitivity of runoff to different climatic variables, including temperature, precipitation, and potential evapotranspiration.

Section snippets

Baseline period

The first step to ascertain the impacts of human activities and climate variability on runoff changes is determining the baseline period. There are two approaches for determining the baseline period i) the human-designated (Miao et al., 2011, Xu et al., 2006) and ii) the abrupt change detecting (Liang et al., 2015). In the human-designated, an available period with the lowest human interference will be considered a baseline period and the post-baseline period is selected based on observations

Baseline period determination

Table 2 provides the trend of temperature, precipitation, potential evapotranspiration, and runoff from MMK in the Ghaleh-Shahrokh and Javanmardi watersheds. The results in the Ghaleh-Shahrokh watershed indicate that there is no significant trend in precipitation and potential evapotranspiration. However, the temperature has increased substantially at 1% significance level. Additionally, runoff in the Ghaleh-Shahrokh watershed has decreased at 1% confidence level. In the Javanmardi watershed,

Discussion

The summary of the obtained results from 9 different methods in two study areas is illustrated in Fig. 5. There are stark differences between the principles and structure of these methods. Generally, calculating the relative contribution of human activities and climate variability to runoff changes using empirical methods is easy. However, these methods do not consider the physical mechanisms of runoff generation. These methods need long-term hydrological and precipitation data to create

Conclusions

Determination of possible runoff changes in response to climate variability and anthropogenic changes is very substantial for water resources management, especially in arid and semi-arid regions. This study used three main categories, including empirical methods, elasticity-based methods, and hydrological modeling to determine the relative contribution of anthropogenic changes and climate variability effects on runoff changes in two watersheds in the central plateau of Iran, including

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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