Spatial distribution of δ2H and δ18O values in the hydrologic cycle of the Nile Basin

Abstract

Existing δ 2 H and δ 18 O values for precipitation and surface water in the Nile Basin were used to analyze precipitation inputs and the influence of evaporation on the isotopic signal of the Nile River and its tributaries. The goal of the data analysis was to better understand basin processes that influence seasonal streamflow for the source waters of the Nile River, because climate and hydrologic models have continued to produce high uncertainty in the prediction of precipitation and streamflow in the Nile Basin. An evaluation of differences in precipitation δ 2 H and δ 18 O values through linear regression and distribution analysis indicate variation by region and season in the isotopic signal of precipitation across the Nile Basin. The White Nile Basin receives precipitation with a more depleted isotopic signal compared to the Blue Nile Basin. The hot temperatures of the Sahelian spring produce a greater evaporation signal in the precipitation isotope distribution compared to precipitation in the Sahara/Mediterranean region, which can be influenced by storms moving in from the Mediterranean Sea. The larger evaporative effect is reversed for the two regions in summer because of the cooling of the Sahel from inflow of Indian Ocean monsoon moisture that predominantly influences the climate of the Blue Nile Basin. The regional precipitation isotopic signals convey to each region's streamflow, which is further modified by additional evaporation according to the local climate. Isotope ratios for White Nile streamflow are significantly altered by evaporation in the Sudd, but this isotopic signal is minimized for streamflow in the Nile River during the winter, spring and summer seasons because of the flow dominance of the Blue Nile. During fall, the contribution from the White Nile may exceed that of the Blue Nile, and the heavier isotopic signal of the White Nile becomes apparent. The variation in climatic conditions of the Nile River Basin provides a means of identifying mechanistic processes through changes in isotope ratios of hydrogen and oxygen, which have utility for separating precipitation origin and the effect of evaporation during seasonal periods. The existing isotope record for precipitation and streamflow in the Nile Basin can be used to evaluate predicted streamflow in the Nile River from a changing climate that is expected to induce further changes in precipitation patterns across the Nile Basin.

Mid‐Holocene environmental change and human occupation at Sai Island, Northern Sudan

“…Although we do not find values this low in Areas A or B, evaporative enrichment of locally sourced meteoric water or floodwater from the Nile could account for this discrepancy. The modern Nile in Cairo has a δ 18 O of 2.3‰ (SMOW; Iacumin, Bocherens, Mariotti, & Longinelli, 1996), even higher than modern rainfall in Sudan (however, substantially lower δ 18 O values are observed upstream of Aswan (Langman, 2015).…”

“…(VPDB), given the current Khartoum mean annual temperature of 28°C (Neumann, 1989 Iacumin, Bocherens, Mariotti, & Longinelli, 1996), even higher than modern rainfall in Sudan (however, substantially lower δ 18 O values are observed upstream of Aswan (Langman, 2015).…”

Sustainable water resources development and management in large river basins: an introduction

“…It has two main tributaries, the White Nile and the Blue Nile (Melesse et al 2014 ). The Blue Nile, which originates from the Ethiopian Plateau, is the source of most of the water and nutrients in the lower reach of the Nile (Langman 2015 ), though the White Nile is the longest tributary of the Nile (Fig. 4 ).…”

“…The Nile Basin covers an area of approximately 3.11 million km 2 , and flows through nine countries. It is an international river that spans the most countries in Africa (Langman 2015 ). The Nile River has very limited water resources, and its annual average runoff is only 84 billion m 3 .…”

Geographic variations in the slope of the δ 2 H – δ 18 O meteoric water line over Europe: a record of increasing continentality

“…Therefore, they have been recognized for decades as powerful natural tracers of the water cycle (Craig 1961;Craig & Gordon 1965;Dansgaard 1964;Rozanski et al 1993;Gat 1996;Gat et al 2001;Rozanski 2005).  2 H and  18 O of meteoric waters have been extensively used to identify the main sources of water evaporation (Merlivat & Jouzel 1979;Uemura et al 2008), migration pathways of humid air masses (Masson-Delmotte et al 2005;Vimeux et al 2005;Guan et al 2013), temperature effects under temperate climates (Dansgaard 1964;Yurtsever 1975;Rindsberger et al 1983;Rozanski et al 1993;Gat 1996), amount effects under humid tropical and equatorial areas (Dansgaard 1964;Rozanski et al 1993), and the recycling of continental moisture released during the evaporation of soils, rivers, lakes and closed marine basins (Gat & Carmi 1970;Froehlich et al 2008;Wang & Yakir 2000;Gibson & Edwards 2002;Aemisegger et al 2014;Langman 2015;Wang et al 2016;Juhlke et al 2019). Craig (1961) and refined later by Dansgaard (1964) who considered mean isotopic compositions weighted by the amount of precipitation.…”