Water demand for irrigation may be lower in the future

Large areas of instability have spread across the state in recent months. The volume of rain exceeded the normal average in several regions, and the perception of higher temperatures during winter has increased. Although it is not possible to say with certainty whether these are climate changes or whether they are just aspects of natural variability, developing strategies to minimize the effects of climate change is increasingly important.

This is what the thesis carried out by the researcher shows Tirzah Moreira, with guidance from the teacher José Antônio Louzada, from UFRGS Hydraulic Research Institute (IPH), and with the co-guidance of Olaf Pedrollo. The study titled Trends in extreme indices and seasonal analysis of precipitation and temperature in the northwest region of Rio Grande do Sul - increase in temperature and climate change until the end of the century sought to determine whether greater or lesser amounts of water for irrigation will be needed in the future compared to the current period. “Many reasons encouraged the choice of the theme. Firstly, IPH participated in a large project that addressed climate change, as one of its objectives was to estimate the likely future flows in the rivers of the 12 large Brazilian hydrographic basins, where there are hydroelectric projects in addition to those already known to be built by 2030”, says Tirzah.

The purpose of the work was to produce an investigation to detect changes in temperature and precipitation in the northwest region of Rio Grande do Sul. It was carried out using a hydrological model that verifies the water balance at the soil-plant-atmosphere interface, known as SWAP . Soil sampling was carried out in the municipality of Pejuçara, and seven different locations in the region were considered. The climate variables used by SWAP were generated by climate models for both the current period (in the study, 1961-1990) and the future period (2011-2100). To generate this information, the model needs to make assumptions about the future composition of the atmosphere, based on the behavior of relationships between human activities and the environment, such as the use of fossil fuels, economic development models and environmental concerns.

Agriculture was the focus of the thesis, as the state has been recording increasing losses in grain harvests: “It is estimated that half of production was lost from November 2011 to August 2012, with the northwest region being the hardest hit. Looking at the other extreme, it is also clear, over the last decade, that intense rain events, with consequent floods and material losses in cities, are becoming more frequent”, adds Tirzah.

The frequency and intensity of extreme rainfall events using different precipitation indices were also investigated. Research indicated an increase of 3°C in the annual average by the end of the century, as well as an increase in the amount of rain. From these projections, lower demands for water for irrigation in the future appeared: “In this way, both positive and negative impacts can result. Positive if this increase in precipitation is well distributed throughout the year and can meet, without loss, the water needs of soybeans. And negative if this increase in precipitation occurs in a concentrated way, in the form of extreme events”, explains the researcher. Tirzah also draws attention to other impacts of climate change on agriculture, such as the occurrence of hail, windstorms and very intense rains, which can destroy crops.

Faced with all these challenges, research proves to be fundamental to estimate future water demands for irrigation and improve them: “Studies like this leave the perspective that, if agricultural production must grow to support a population that is also growing throughout of the century, so there is an immediate need to mitigate the impacts that could arise from a changing climate”, concludes Tirzah.

Scientific article

Melo, Tirzah Moreira de; Louzada, Jose Antônio; Pedrollo, Olavo. Trends in Extreme Indices and Seasonal Analysis of Precipitation and Temperature in the Northwest Region of Rio Grande do Sul, Brazil. American Journal of Climate Change, vol. 4, p. 187-202, 2015

Tese

Degree: Stochastic simulation of the impacts of climate change on water demands for irrigation in the northwest region of Rio Grande do Sul
Author: Tirzah Moreira de Melo
Advisor: José Antônio Saldanha Louzada
Unity: Postgraduate Program in Water Resources and Environmental Sanitation