Pluviometric and fluviometric trends in association with future projections in areas of conflict for water use

Highlights

• The seasonality in the precipitations were not determinant in the flow data trends

• There was a tendency to reduce the annual minimum flow in all fluviometric stations

• Behavior of the stream flows are associated with the increased demand for water use

• Future flows showed a downward trend, as well as flows observed

• This method has great potential to the solution of water resource management

Abstract

Rapid population growth coupled with climate change has been putting pressure on natural resources worldwide, especially on water resources. The Paracatu basin located in Brazil is a basin which has been showing a reduction in its water availability for many years due to the growing demand for irrigation in the region. Therefore, the objective of the present work was to analyze the trends in the flow and precipitation data for the Paracatu basin and correlate them with land use between the years 1980 and 2019, and thus make a projection of flows through the year 2030 based on these results. The projections of future flows in the fluviometric stations analyzed were obtained using the WEAP model, considering the projected increase in the irrigated area for the region and the future climate data from the IPCC for the RCP 4.5 scenario. The results of the analyzes indicated a tendency towards a reduction in flows in all the analyzed fluviometric stations, both in the monthly and annual series, whereas the total annual precipitation did not show a trend in the analyzed period. Future flows showed a downward trend, as well as flows observed in the period from 1980 to 2019, reinforcing that activities such as irrigated agriculture without planning can negatively affect the sustainability of water resources, intensifying conflicts and tensions which already exist in the basin. This type of analysis proved to have great potential to contribute to the solution of water resource management challenges in several hydrographic basins around the world which are in a situation of scarcity and conflict.

Introduction

Water is the most important resource of agricultural, industrial and services (Zarei et al., 2020). According to the World Water Assessment Programme – WWAP (UNESCO, 2016) global demand for water is expected to increase by 55% by 2050, and as predicted by the United Nations (UN), if current consumption patterns continue until 2025, approximately one third of the world's population will suffer from chronic water scarcity (Shinde, 2005).

It is currently known that the Brazilian population will show significant growth until the next century (IBGE - Instituto Brasileiro de Geografia e Estatística, 2018). This growth is combined with a demand for food, material goods and water (Dias et al., 2016). This situation in developing countries like Brazil is even more representative, since problems related to drinking water and basic sanitation are common in some places, as well as the proper use of water (Bouwer, 2000; Zarei et al., 2020). Furthermore, the increasing use of water in irrigated agriculture and industry development combined with the climatic changes registered in the last decades have promoted progressive pressure on water resources on almost the entire terrestrial globe (Lima et al., 2019; Safavi, Hamid R. Golmohammadi, Mohammad H. Sandoval-Solis, 2015; Tubiello et al., 2015).

Demand for water, whether for domestic consumption, irrigation or electricity production, results in a panorama where compatibility between uses is necessary in order to balance human needs and those of the ecosystems in which they are inserted. Thus, understanding the trend of water use together with economic development is essential to predict future water demand, and thus develop strategies which are appropriate in each situation (Sun and Fang, 2018).

The analysis of changing patterns in environmental science is widely studied by trend detection tools in time series (Mhiribidi et al., 2018; Sun and Fang, 2018; Zhang et al., 2018). The analysis of water availability in space and time promotes subsidies for managing the rational use of water, reducing the risks of crop loss and productivity through decision-making directed towards efficient planning and sustainable use of water (Lima et al., 2019).

The Paracatu basin stands out among several Brazilian hydrographic basins which present a current unsustainable scenario in the use of water resources for its intense agricultural activity, mainly being irrigated agriculture. This basin has presented significant changes in land use over the last decades, such as the replacement of native vegetation areas by cultivation areas or pastures.

Irrigated agriculture is the sector which consumes the most water, constituting 90% in developed countries (Zarei et al., 2020), and not differing in the hydrographic basin of the Paracatu, being responsible for more than 78% of the demand (Pruski et al., 2007), and occupying an area of approximately 123,000ha (ANA - Agência Nacional de Águas, 2015); a factor which over time has provided a framework for conflict over the use of water in the region (Assaf et al., 2008; Novaes et al., 2009; Pruski et al., 2007; Rodriguez et al., 2007; Wehling, 2016). Conflicts over the use of water in the Paracatu basin occur in a punctual way due to the quantitative aspect, meaning that the demands have no uniform distribution neither in time nor in the space of the basin, being concentrated in some sub-basins.

Studies carried out in the basin have shown that the available overall flow met the total water demands (Pruski et al., 2007), however there is a need for more recent studies for the current diagnosis and future projection.

Long records of hydrological data show the temporal variation in the flow, and the analyzes of these series can decipher the cause of the variation, being influenced by climatic changes as well as by human activities. In addition, many hydrological models analyze the response of the flow process caused by climatic and human actions. Even though these are powerful tools, hydrological models have numerous uncertainties caused by deficiency of structure, calibration of parameters and scale problems associated with the hydrological model (Zhang et al., 2011). Therefore, studies which correlate the behavior of flows over time together with predictions of future flows from hydrological models provide support for management policies, and make it possible to identify regions which present greater pressures on water resources.

Specialists in water resource planning and management believe that modeling is a fundamental requirement which facilitates the application of Integrated Water Resource Management at the level of river basins; in this sense, the Water Evaluation and Planning System (WEAP) model can be used, which enables performing future projections considering several scenarios (Hong et al., 2016; Kou et al., 2018).

In the scenario of climate uncertainty, the IPCC formed the current basis of physical science for climate change, and created a total of four scenario projections, from optimistic to pessimistic. The scenarios are called RCPs, standing for Representative Concentration Pathways. These scenarios are based on the evolutionary history of several factors such as the concentration of greenhouse gases and type of land use (Beck and Mahony, 2017; Collins et al., 2013; IPCC, 2014; Liuzzo et al., 2017; Newman, 2017).

In view of the above, the present study aimed to analyze trends in flow and precipitation data in the Paracatu basin and to correlate them with the land use in the period from 1980 to 2019, and to make a projection of the average flows until the year 2030, considering the increase in water demand and climate change according to IPCC RCP 4.5.