Future Global Rainfall Erosivity in 2050 and 2070

Introduction

The erosive force of rainfall (rainfall erosivity) is a major driver of soil, nutrient losses worldwide and an important input for soil erosion assessments models. Here, we present a comprehensive set of future erosivity projections at a 30 arc-second (~1 km2) spatial scale using 19 downscaled General Circulation Models (GCMs) simulating three Representative Concentration Pathways (RCPs) for the periods 2041–2060 and 2061–2080.

Future climate projections give a pessimistic outlook on soil erosion and its associated impacts, which include increased land degradation, a loss of agricultural productivity and soil carbon losses. Moreover, soil’s ability to offset and buffer global warming in the future through carbon sequestration is reduced by soil erosion. A recent Intergovernmental Panel on Climate Change (IPCC) report highlights the anticipated acceleration of global land degradation due to increasing rates of soil erosion and losses of soil organic carbon. Increasing temperatures combined with changing rainfall patterns, and intensification of rainfall will likely be the main drivers of this process. The interactions between rainfall and soil play a vital role in the ecological, hydrological and biogeochemical cycles occurring on land. Climate change is expected to alter the attributes of rainfall due to the increase in atmospheric specific humidity in future warmer climate states , and due to changes in seasonal precipitation . In a more energetic climatic state, an intensification of the hydrological cycle and associated extreme precipitation and runoff will likely have important impacts on the surface processes governing the functionality and loss of soils . Future climate change is expected to further influence rainfall intensity, as well as the magnitude and frequency of rainfall events . Studies have emphasized the nonlinear response of soil erosion to changing rainfall amount and intensity due to the importance of runoff in eroding soil. The impact of these hydrological driving forces on soil erosion will be exacerbated or reduced depending on the resilience of the land characteristics (e.g. plant biomass and residue, soil physical characteristics, land use) to buffer their effect in future climatic states .

Global Rainfall Erosivity projections 2050 and 2070

For the climatic state in 2050, the mean estimation derived from the 19 model endmembers projects a global average rainfall erosivity value in the range of 2,765 – 2,822 MJ mm ha^-1 h^-1 yr^-1. The range of values is due to the dependency on the RCP scenario, with RCP2.6 increasing erosivity by 26.2%, RCP4.5 by +27.6% and RCP8.5 by 28.8% compared to the 2010 baseline. For 2070, the global average rainfall erosivity is predicted in the range of 2,782 – 2,942 MJ mm ha^-1 h^-1 yr^-1, an increase of 27% in the case of RCP2.6, 30% for RCP4.5 and 34.3% for RCP8.5 compared with the 2010 baseline.

The Northern Hemisphere shows larger increases compared with the Southern Hemisphere for the period 2010–2050, the latter of which has relatively broader areas experiencing decreased rainfall erosivity. Interestingly, the red line representing the mean latitudinal change (%) also has a higher variation in the Northern compared with the Southern hemisphere. This is a manifestation of the increased spatial complexity of the changing precipitation patterns in the Northern Hemisphere. The average change in rainfall erosivity in the Northern Hemisphere under the RCP2.6 scenario shows 2 distinct latitudinal peaks. These peaks occur between 59 and 65◦N and 15-28◦N, representing the large percentage changes in rainfall erosivity in cold and arid climate zones. The latitudinal zones between these peaks show a lower relative magnitude of change, particularly the zone between 30 and 45◦N where the magnitude of change is limited to roughly 25%. In the Southern Hemisphere, the variability in the change in rainfall erosivity with latitude is relatively lower. The mean increase in rainfall erosivity across the upper part of the hemisphere (0-40◦S) is roughly 10%, as Central Africa and North Latin America have mixed trends. Between 2050 and 2070, the magnitude of change in rainfall erosivity is reduced compared to the period between 2010 and 2050.

Figure 1.Geographical distribution of erosivity changes for RCP2.6 for both 2010–2050 (a) and 2050–2070 (b). Right graphs represent the latitude change with percentage distribution per class (bottom axis); the red line is the mean % change (Top axis).

Model predictions for Rainfall Erosivity in 2050 and 2070

We employed an ensemble approach by accounting for the outputs of all available endmember models. This approach predicts the average magnitude of change in a robust manner, as well as allowing the uncertainty associated with model endmember (dis)agreement to be better accounted when predicting future rainfall erosivity. RCP scenario as a result of the different CMIP5 endmember simulations. Comparing global erosivity in 2050 to the 2010 baseline, only one RCP2.6 model endmember estimates an increase of<22% while the majority predict an increase in the range of 25–29%. In the most pessimistic scenario of RCP8.5, only two models predict an increase of <25% whereas seven models project an increase in the range of 30–36% (Fig 2 left). The description of the models canbe found either in the article or in the supplementary material.

The lower boundary is the RCP2.6 scenario and the upper boundary is the RCP8.5 scenario. The highly increasing trends in the global mean are driven by changes in specific climatic zones, mostly attributed to the elevated rainfall erosivity in arid (60–79%) and cold zones (76.5–118.7%). These two zones occupy 68% of the earth surface  and therefore drive a large percentage change in the global mean, most evident in the Northern Hemisphere. The proportion of semi-arid land with large changes in rainfall is greater than for tropical land as a whole. In particular, the projections of increased rainfall erosivity in arid zones in 2050 is driven by increased rainfall in the Sahel region, arid parts of Australia and the Middle East. In cold zones, the climate dynamics in Siberia and the intensification of rainfall in North America  will drive the increased erosivity. The tropical and temperate climatic zones show a percentage increase in rainfall erosivity between 14.5 and 22.1% depending on the RCP scenario (Fig 2 right).

Figure 2. Left:The range of model predictions (the left boundary is the RCP2.6 prediction and the right is the RCP 8.5) for years 2050. Right: Projections of erosivity change (aggregated values and %) for the five climatic zones per scenario (RCP2.6, RCP8.5) and two periods (2010-2050, 2050-2070). The percentage figures for 2050 and 2070 in each climatic zone represent the % change compared to 2010 baseline corresponding to the lesser erosive RCP (bottom) and more erosive RCP (top).

The model predictions were successfully compared with 20 regional studies addressing the rainfall erosivity projections. Therefore, we did a review of the most updated 20 studies on future rainfall erosivity. More information in the section 4.4. of article and the Additional Material.

Data

Download all the data (aggregated and per scenario)

Reference

Panagos, P., Borrelli, P., Matthews, F., Liakos, L., Bezak, N., Diodato, N. and Ballabio, C., 2022. Global rainfall erosivity projections for 2050 and 2070. Journal of Hydrology, Art.no.127865.DOI: 10.1016/j.jhydrol.2022.127865