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NNadir

(33,368 posts)
Sun Jan 19, 2020, 06:20 PM Jan 2020

Importance and vulnerability of the world's water towers.

The paper I'll discuss in this post is this one: Importance and vulnerability of the world’s water towers (W.W. Immerzeel et al Nature volume 577, pages 364–369 (2020).

One of the greatest risks of climate change, beyond rising seas and extreme weather, both of which are well known, is the risk to humanity's water supplies. In a lecture I attended last year, I learned that about 10% of the observed sea level rise at this point, actually involves the pumping of fossil groundwater - for example on the Ogalalla acquifer in the American midwest - which ultimately ends up in the seas. We are all familiar with the issue of arctic ice melts, but perhaps less familiar with the consequences of mountain ice melts. Here, as the authors note in the introduction, the term "Water Tower" refers to mountain range glaciation which provides fresh water for a large proportion of the world's population. From the paper's introduction:

The term ‘water tower’ is used to describe the water storage and supply that mountain ranges provide to sustain environmental and human water demands downstream1,2. Compared to its downstream area, a water tower (seasonally) generates higher runoff from rain as a result of orographic precipitation and delays the release of water by storing it in snow and glaciers (because of lower temperatures at high altitude) and lake reserves. Because of their buffering capacity, for instance by supplying glacier melt water during the hot and dry season, water towers provide a relatively constant water supply to downstream areas. We define a water tower unit (WTU; see Methods, Extended Data Fig. 1) as the intersection between major river basins5 and a topographic mountain classification based on elevation and surface roughness6. Since water supply and demand are linked at the river basin scale, the basin is the basis for the WTU. One WTU can therefore contain multiple topographically different mountain ranges and we assume that it provides water to the areas in the downstream river basin that are hydrologically connected to the WTU (Extended Data Fig. 1, Extended Data Table 1 and 2). Subsequently, we consider only cryospheric WTUs by imposing thresholds on satellite-derived snow-cover data7 and a glacier inventory8, because the buffering role of glaciers and snow and the delayed supply of melt water is a defining feature of water towers. Consequently, there are regions (for example, in Africa), which do contain mountain ranges, but because of their small snow and ice reserves they do not meet the WTU criteria. In total, we define 78 WTUs globally (see Methods), which are home to more than 250 million people. However, more than 1.6 billion people live in areas receiving water from WTUs, which is about 22% of the global population9 (Fig. 1).


The authors have also defined WTI, the "Water Table Index" in the abstract, which is open sourced, but for convenience I'll repeat it here:

Here we present a global water tower index (WTI), which ranks all water towers in terms of their water-supplying role and the downstream dependence of ecosystems and society.


The news, of course, is not good:

Water towers have an essential role in the Earth system and are particularly important in the global water cycle1,2. In addition to their water supply role, they provide a range of other services10,11. About 50% of the global biodiversity hotspots on the planet are located in mountain regions12, they contain a third of the entire terrestrial species diversity13, and are extraordinarily rich in plant diversity14. Moreover, mountain ecosystems provide key resources for human livelihoods, host important cultural and religious sites, and attract millions of tourists globally6. Economically, 4% and 18% of the global gross domestic product (GDP) is generated in WTUs and WTU-dependent basins respectively15. Furthermore, mountains are highly sensitive to climate change3,4 and are warming faster than low-lying areas owing to elevation-dependent warming16. Climate change therefore threatens the entire mountain ecosystem. Worldwide, the vast majority of glaciers are losing mass17, snow melt dynamics are being perturbed18,19,20,21, and precipitation and evapotranspiration patterns are shifting, all leading to future changes in the timing and magnitude of mountain water availability22. Besides, the combination of cryosphere degradation and increases in climate extremes implies changing sediment loads affecting the quality of water supplied by mountains23.


In the economic impact, the paper does not mention hydroelectricity, which trails only biomass combustion - which is responsible for about half of the world's 6 to 7 million air pollution deaths per year - as the world's largest form of so called "renewable energy."

The threat to these two forms of so called "renewable energy" should raise a question in one's mind about how sensitive this stuff is to um, weather, weather that is strongly affected by the failure of this popular madness to be effective at addressing climate change. (There is a reason that humanity stopped depending on the weather for energy, beginning in the 19th century, not that reactionaries ever look at the historic results of their evocations. Santayana and all that.)

Anyway, some graphics from the paper:



The caption:

The WTI, derived from the SI and the DI, is shown for all 78 WTUs, in combination with the shaded total population in all WTU-dependent river basins. Labels indicate the five water towers with the highest WTI value per continent. The insets show the number of people living in WTUs as a function of elevation and of the downstream population’s proximity to the WTUs9.


The authors note that the effects of the destruction of mountain glaciers may also impact the frequency of natural disasters; it's not all about hurricanes and fires:

Not only are the world’s water towers crucial to human and ecosystem survival, the steep terrain in combination with extreme climatic conditions, and in some regions seismic or volcanic activity, frequently triggers landslides, rock fall, debris flows, avalanches, glacier hazards and floods24,25. Since 2000, over 200,000 people have died in WTUs as a result of natural disasters26. Climate change, in combination with population growth, urbanization and economic and infrastructural developments, is likely to exacerbate the impact of natural hazards and further increase the vulnerability of these water towers23,27,28,29,30.


Well, none of that is likely to be a serious as Fukushima. How many people died from radiation at Fukushima again? I ask people all the time when they mention this event to me, and I never get a straight answer, if in fact, I get an answer at all. I happen to know that about 15,000-20,000 people from the part of that event that no one gives a rat's ass about - the tsunami - were killed by seawater but somehow the only area of concern is escaped radioactive materials.

The authors, in seeking to quantify effects define something called a "supply index" (SI):

The supply index (SI) is based on the average of four indicators that are quantified for each WTU: precipitation, snow cover, glaciers and surface water (Fig. 2a, Extended Data Table 3, Supplementary Table 1 and Methods). If the precipitation in the WTU (Extended Data Fig. 3a) is high relative to the overall basin precipitation and if the inter-annual and intra-annual variation is low (that is, the supply is constant), a WTU scores highly on the precipitation indicator. If a WTU has persistent snow cover (Extended Data Fig. 3b) throughout the year and the snowpack shows lower inter-annual variation, this will result in a high snow indicator. Similarly, if the total glacier ice volume (Extended Data Fig. 4a) and glacier water yield in a WTU are high relative to the basin precipitation then a WTU has a high glacier indicator value...


...and then a "Demand Index," (DI):

To derive a demand index (DI) for each WTU, we quantify the monthly water requirements to be supplied by the water towers to sustain the WTU basin’s net sectoral water demand for irrigation, industrial (energy and manufacturing) and domestic purposes, and monthly natural water demand, relative to the total annual demand (Fig. 2b, Extended Data Table 4, Supplementary Table 1). Monthly sectoral water requirements are estimated by subtracting the monthly water availability downstream (ERA5 precipitation minus natural evapotranspiration32) from the monthly net demands33. The DI is the average of the four indicators (see Methods). Figure 2b demonstrates considerable variability, globally and within continents, in the demands that WTUs need to sustain. Irrigation water demands are the highest of the four demand types, and this is relatively consistent across the continents. The Asian river basins, specifically the heavily irrigated and densely populated basins such as the Indus, Amu Darya, Tigris, Ganges-Brahmaputra and Tarim, score more highly on the DI than other basins across the world and they score highly on each sectoral demand indicator. In those basins, the water required to close the gap between demand and downstream supply may also originate from (unsustainable) groundwater use34,35.


This graphic touches on these indexes:



The caption:

a, b, The SI (a) and the DI (b) of each WTU grouped by continent and ordered by SI or DI value, respectively. The stacked bars show the four indicator values for surface water (L), glacier (G), snow (S) and precipitation (P). In b, the stacked bars show the four indicator values for natural (DNAT), industrial (DIND), domestic (DDOM) and irrigation demands (DIRR). Calculation details of the indicators and indices are provided in Extended Data Tables 3, 4.


There is a discussion of the risks to humanity, not that humanity is as important as the stock prices of the Tesla car company, with a focus on the vulnerable Indus valley:

Vulnerability of the water towers
We assess the vulnerability of each WTU and show this for the five most important (that is, with highest WTI values) WTUs in Asia and Oceania, Europe, North America and South America (Fig. 3, Supplementary Table 2). For this analysis, we include the hydro-political tension37, baseline water stress38, government effectiveness39, projected climate change40, projected change in GDP41, and projected population change9 (see Methods). The highest-ranking WTUs of South America and Asia in particular are more vulnerable than those in North America and Europe. Strikingly, the Indus, which is globally the most important water tower (Fig. 4), is also very vulnerable. The Indus is a transboundary basin with considerable hydro-political tension between its riparian countries Pakistan, India, China and Afghanistan. The population of approximately 235 million people in the basin in 2016 is projected to increase by 50% by 2050, and the basin’s GDP is projected to encounter a nearly eightfold increase41. The average annual temperature in the Indus WTU is projected to increase by 1.9?°C between 2000 and 2050, compared to 1.8?°C in the downstream section40. The average annual precipitation in the Indus WTU is projected to increase by 0.2%, compared to 1.4% downstream40. It is evident that, owing to the expected strong growth in population and economic development, the demand for fresh water will rise exponentially42. Combined with increased climate change pressure on the Indus headwaters, an already high baseline water stress and limited government effectiveness, it is uncertain whether the basin can fulfil its water tower role within its environmental boundaries. It is unlikely that the Indus WTU can sustain this pressure.


The next graphic attempts to evoke a feel the types of risks:



The caption:

The total vulnerability (indicated by larger polygons), and projected change indicators of the five most important WTUs on each continent. BWS is the baseline water stress indicator of the basin38; GE is an indicator for government effectiveness in the basin39; HT is hydro-political tension37; dGDP41 and dPop9 are the projected changes in gross domestic product and population between 2000 and 2050, according to Shared Socioeconomic Pathway 2 (SSP2)67; dP40 and dT40 are the projected precipitation and temperature changes between 2000 and 2050 according to the CMIP5 multi-model ensemble mean for Representative Concentration Pathway (RCP) 4.540. WTUs are ranked by vulnerability (highest vulnerability on top); colour filling indicates the WTU’s WTI value. See Methods for calculation details.


And then a graphic cartoon focuses on the Indus:



The caption:

a, The supply and demand indicators. b, The vulnerabilities. See Methods for details on the supply and demand indicators and the meaning of the vulnerability ranges. ST, snow cover; SMV, intra-annual snow cover variability; SYV, inter-annual snow cover variability; S, snow indicator; SL, lake and reservoir volume; L, surface water indicator; GV, glacier ice volume; PGLAC ? B, glacier water yield; G, glacier indicator; PWTU, WTU precipitation; PBAS, basin precipitation; PMV, WTU intra-annual precipitation variability; PYV, WTU inter-annual precipitation variability; P, precipitation indicator; DIND,y, net industrial demand; DIND, industrial demand indicator; DNAT,y, natural demand; DNAT, natural demand indicator; DDOM,y, net domestic demand; DDOM, domestic demand indicator; DIRR,y, net irrigation demand; DIRR, irrigation demand indicator.


But of course, the Indus is not the only area to be affected:

The Indus does not stand alone, however. Nearly all important WTUs in Asia are also highly vulnerable (Fig. 3). Most WTUs are transboundary, densely populated, heavily irrigated basins and their vulnerability is primarily driven by high population and economic growth rates and, in most cases, ineffective governance. Moreover, the Syr Darya, Amu Darya and Indus, in particular, are characterized by considerable hydro-political tension37. In most cases, downstream riparian states are dependent on mountain water resources provided by bordering upstream states to supply the competing irrigation, hydropower and domestic demands. In South America, the vulnerability is less than for the Asian WTUs, and the drivers are variable. On northern Chile’s Pacific coast, the baseline water stress and a projected decrease in precipitation (?4.8%) cause the vulnerability, whereas population and economic growth render the La Puna region’s WTU vulnerable. In North America, the vulnerabilities are related to population growth and temperature increase.


The 34 authors of the paper sign off on this wishful thinking statement:

We therefore make three essential recommendations. First, mountain regions must be recognized as a global asset of the Earth system. Second, it must be acknowledged that vulnerability of the world’s water towers is driven both by socio-economic factors and climate change. Third, we must develop international, mountain-specific conservation and climate-change adaptation policies (such as national parks, pollutants control, emission reductions, erosion control and dam regulations) that safeguard the mountain ecosystems and mountain people and simultaneously ensure water, food and energy security of the millions of people downstream.


Don't worry. Be happy. Forget all that stuff. It doesn't involve you. Be happy. Someday maybe you can fly off to Mars on Elon Musk's rocket ship.

Have a nice Sunday evening.
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