The global water cycle is undergoing continuous and major perturbation what regards for example spatio-temporal changes in intensity and frequency of extreme events of flooding and wet-dry periods of land. Our understanding about climate changes has improved enormously, through the advances in GCM ‘Global Climate Models’, e.g. the predictions of tipping points in the earth’s system and associated severe heatwaves due to increase in temperature from the continuous emissions of greenhouse gases. Yet our knowledge on the impacts of climate change on the water global cycle is still improving specially the uncertainties mentioned above which is important for developing a sustainable-resilient agro- and food production.
New research is indicating that heat-induced global water cycle changes pose significant challenges to global ecosystems, soil stability and desertification, agro-food industries and human society in general. Indeed, quantifying historical water cycle change though very important to understand and assess , it is difficult owing to shortage of direct observations. In particularly over the ocean, where major parts of global precipitation and evaporation occur in the world oceans. Researchers have found new tools to improve our knowledge about key parameters processes associated with changes in the global water cycle. Air–sea fluxes of freshwater imprint on ocean salinity such that mean salinity is lowest in the warmest and coldest parts of the ocean, and is highest at intermediate temperatures. These findings were used to track salinity trends in the warm, salty fraction of the ocean, and quantify the observed net poleward transport of freshwater in the Earth system from 1970 to 2014. It was found that poleward freshwater transport from warm to cold ocean regions has occurred at rates that is not replicated in the current generation of climate models. Should this be the case, the implication is that the historical surface flux amplification is weaker climate models compared to observations. The results establish historical constraint on the poleward freshwater transport that will assist in addressing biases in climate models (https://www.nature.com/articles/s41586-021-04370-w) and thereby help us to better predict the behaviour and details in the global water cycle.
Climate change will therefore be intensifying the Earth’s water cycle at twice the predicted rates (https://amp.theguardian.com/environment/2022/feb/24/climate-change-is-intensifying-earths-water-cycle-at-twice-the-predicted-rate-research-shows; https://newsroom.unsw.edu.au/news/science-tech/global-warming-amplifying-our-water-cycle-and-its-happening-much-faster-we). Rising global temperatures and the increasing amount of heat have shifted at least twice the amount of freshwater from warm regions towards the Earth’s poles than previously thought as the water cycle intensifies, according published analysis in Nature. In the future there will be more rain but less water as this is shown from Climate projections suggesting that, by end of the century, the amount of rain for example in the Upper Nile basin could increase by up to 20%. A new paper by the same group, shows that, despite more rainfall, devastating hot and dry spells are projected to become more frequent in the Upper Nile basin (https://theconversation.com/in-the-future-there-will-be-more-rain-but-less-water-in-the-nile-basin-129360?utm_medium=ampemail&utm_ source=email).
These trends in the global water cycle demonstrate that ‘RENEWABLE SOIL TECHNOLOGIES’ need to take in consideration the impacts of climate change on agriculture and agro-industries by being directly dependent on the renewable water resources. The Nile in general – world’s longest river – runs through 11 countries in Africa and its basin covers about 3 million sq kms, i.e. about 10% of the continent’s landmass. A huge population, about 250 millions people, is dependent on the Nile in Ethiopia, Uganda, South Sudan, Sudan and Egypt. Almost all of the rainfall falls and feeds upstream countries of the Blue and White Nile – in the upper Nile (South Sudan, western Ethiopia and Uganda). While the lower Nile basin receives very little rainfall (Sudan and Egypt) and thereby depends heavily and directly on the Nile for water. Climate projections by the end of the 21-century, suggest that the rain in the Upper Nile basin could increase by up to 30%. However, despite more rainfall, the devastating hot and dry spells are projected to become more frequent in the Upper Nile basin.
Currently, about 10% of the basin’s population faces chronic shortages due to seasonal aridity and huge unequal access to water resources. The proportion of population that will face water scarcity will increase to 30% by 2040, i.e. more than 80 million people. These threats from hot and dry conditions will kill crops, reduce hydropower, diminish the water available for people and industry and heighten tensions over the distribution of regional water resources. By 2040, a hot and dry year could push over 45% of the people in the Nile Basin – nearly 110 million people – into water scarcity. In addition to this the population growth would drive water scarcity in the Upper Nile.
In conclusion, climate and population changes in the Nile Basin will project onto an already complex and tense socioeconomic and political landscape.