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Author Topic: General Drought Stuff  (Read 82926 times)

kassy

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Re: General Drought Stuff
« Reply #250 on: June 18, 2020, 09:29:24 AM »
Beyond reasonable drought: New Zealand's climate future

...

NIWA's projections are based on four scenarios, known as representative concentration pathways, published by the Intergovernmental Panel on Climate Change. The pathways range from a best-case scenario of decreasing carbon dioxide concentrations in the atmosphere by 2100, through to a scenario where the levels continue to increase throughout this century.

RNZ has used NIWA's data to visualise two extremes – the number of ‘rain days’ each season, when at least 1mm of rain falls; and ‘hot days’, when the maximum temperature gets over 25 degrees Celsius.

...

Right now in areas like Auckland or Whangārei, there are about 30 days every summer where the mercury shoots up to 25 degrees Celsius or more – roughly one in every three days.

That’s already hotter than it was 50 years ago, when the two cities experienced maybe a dozen ‘hot days’ each summer – balmy beach days interspersed with comfortably warm periods.

By the middle of this century – not all that far away – the number of hot days could nearly double, to 50 a summer. By 2100, within the lifetime of children being born now, nearly every summer day will be a ‘hot day’ in Auckland and Whangārei. The cool days of respite will be over.

Spring rainfall in both places is projected to diminish – meaning it will already be drier when summer begins.

In Northland, even winter rain days are projected to decrease, meaning droughts could become severe, Sood says.

...

https://www.stuff.co.nz/environment/climate-news/300037578/beyond-reasonable-drought-new-zealands-climate-future


and


Climate Change hotspot: MIT study explains why Mediterranean region will witness unique climate trend

A study by the Massachusetts Institute of Technology (MIT) has examined why the Mediterranean region is a hotspot for climate change and found that even with different climate models, the outcome is that within the next few decades, the region would be significantly drier, the institute has said in a statement. The precipitation in the region is likely to reduce by up to 40% during the winter rainy season, the statement added.

....

Despite their differences, the models have been able to agree on the projection for the Mediterranean region, even as the decline in rainfall differs among the models, varying from 10% to 60%. However, before this, the reason behind this projection was inexplicable.

The researchers found that the projected drying up of the region is due to two different consequences of climate change acting together – one is an alteration in the dynamics of the circulation of the upper atmosphere, while the second is a decline in the difference of temperature between land and sea. While neither of these factors would singularly affect the rainfall to such a significant degree, the two effects combined can account for the trend shown by the models, the study believes.

for details:
https://www.financialexpress.com/lifestyle/science/climate-change-hotspot-mit-study-explains-why-mediterranean-region-will-witness-unique-climate-trend/1995368/
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rboyd

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Re: General Drought Stuff
« Reply #251 on: June 20, 2020, 11:31:41 PM »
My rule now is that if any "official" organization such as the IPCC (and all those that rely upon the IPCC estimates) says "2100" they mean "2050". If they say "2050" its "any time after 2030".

This "soft denial" from the official organizations with their reliance on linear models and underestimations of climate sensitivity serve no one well apart from the status quo elites. The next ten years may finally blow that out of the water as the climate system invalidates all their assumptions with reality.

kassy

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Re: General Drought Stuff
« Reply #252 on: July 09, 2020, 04:33:28 PM »
Six hundred years of South American tree rings reveal an increase in severe hydroclimatic events since mid-20th century


Significance
The SADA is an annually-resolved hydroclimate atlas in South America that spans the continent south of 12°S from 1400 to 2000 CE. Based on 286 tree ring records and instrumentally-based estimates of soil moisture, the SADA complements six drought atlases worldwide filling a geographical gap in the Southern Hemisphere. Independently validated with historical records, SADA shows that the frequency of widespread severe droughts and extreme pluvials since the 1960s is unprecedented. Major hydroclimate events expressed in the SADA are associated with strong El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM) anomalies. Coupled ENSO-SAM anomalies together with subtropical low-level jet intensification due to increasing greenhouse gas emissions may cause more extreme droughts and pluvials in South America during the 21st century.

https://www.pnas.org/content/early/2020/07/02/2002411117

Open access

South American background pattern.
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Tom_Mazanec

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Re: General Drought Stuff
« Reply #253 on: July 09, 2020, 07:04:54 PM »
Do we have projected enhanced drought areas for a warmer world? In particular I recall hearing the Plains States would be much drier, is that right?
SHARKS (CROSSED OUT) MONGEESE (SIC) WITH FRICKIN LASER BEAMS ATTACHED TO THEIR HEADS

The Walrus

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Re: General Drought Stuff
« Reply #254 on: July 09, 2020, 07:47:22 PM »
Do we have projected enhanced drought areas for a warmer world? In particular I recall hearing the Plains States would be much drier, is that right?

Drought in the Plains states is strongly correlated with ENSO events, with La Nina years greatly enhancing drought potential.

"Overall, the ECHAM5 simulations indicate a 3.5-fold increase in the odds of summertime severe drought during La Niña compared to El Niño."

"The use of 1050 years of climate simulations representative of recent climate conditions enabled a broader examination of physics, confirming that growing season droughts arise mainly from rainfall deficits, with temperature mostly a response variable through the response of the surface energy exchange with the atmosphere. Conversely, antecedent wintertime meteorological and soil moisture conditions were shown to be of secondary importance to growing season soil moisture. Greater soil moisture persistence was exhibited following the wet season—in October—as opposed to starting before the wet season, March; this is an expression of the memory of the soil moisture to large moisture inputs, relevant for predictability."

https://journals.ametsoc.org/jcli/article/29/18/6783/106934/The-Physics-of-Drought-in-the-U-S-Central-Great

https://www.fws.gov/southwest/es/documents/R2ES/LitCited/LPC_2012/Schubert_et_al_2004.pdf

In a warmer world, ENSO is projected to trend towards greater El Ninos and lesser La Ninas,

kassy

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Re: General Drought Stuff
« Reply #255 on: July 21, 2020, 04:10:35 PM »
Where is the water during a drought?

In low precipitation periods - where and how is the limited available water distributed and what possibilities are there for improving retention in the soil and the landscape? Doerthe Tetzlaff and her team from the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) have discovered that vegetation has a major influence on this. The researchers are investigating the storage, distribution and quality of water in the landscape. Using the example of the drought-sensitive Demnitzer Mühlenfliess in Brandenburg, a sub-catchment area of the Spree, they quantified visible and invisible water flows during and shortly after the drought of 2018.

The annual rainfall in Brandenburg is 560 litres per square metre. This makes Brandenburg a region with the lowest rainfall in Germany. In 2018 there were 390 litres of water per square metre, which is about 40 percent less precipitation than usual.

Even under "normal" climatic conditions, about 90 percent of the precipitation is released back into the atmosphere and does not flow into groundwater or rivers. Groundwater levels in the area today show that the decreased water levels due precipitation deficits from 2018 could not be returned to normal conditions between the growing seasons.

Land use critical for water resource management

Doerthe Tetzlaff is a researcher at the IGB and Professor for Ecohydrology at the Humboldt University of Berlin. She and her team investigated how the process of evaporation and groundwater recharge differ under different soils and land uses.

"Due to the current climate crisis with increasing droughts, we need to know how much water different plants use. As researchers, we ask ourselves: Can we apply sustainable land use to control water consumption and make entire landscapes more resilient towards climate extremes? These findings are the basis for meeting the demands for food production and water supply," says Doerthe Tetzlaff explaining her motivation for her research topic.

Forest soil drier than grassland

In the Demnitzer Mühlenfliess, the team investigated two sites with land uses typical for the region: a mixed forest site with sandy soils and a deep rooting zone; and grassland site with loamier soils and a shallower rooting zone. The forest soil was much drier, which is due to the characteristics of soil and plants.

For example, during the drought, the uppermost metre of the sandy soil in the forest contained only 37 litres per square metre, and under grassland there were as much as 146 litres of water per square metre. The treetops/leaf canopy of the forest shielded part of the rain that evaporated directly from the leaves and never reached the ground. Moreover, the sandy forest soil caused faster water flow through the soil and decreased water storage. Rainfall penetrated deeper into the soil, but was reabsorbed by the trees during the growing season before reaching the groundwater.

Under the grassland, the water continuously recharged the groundwater. The soil could store more water. As the plants only took water from the upper soil, this led to "older" soil water.

"We were able to show how poorly the landscapes in Brandenburg store precipitation, limiting drought resistance. The type of forest we investigated is typical for the Northern European Plain. It was sad to see that even a natural mixed forest is suffering greatly from drought. For economically used forests that are dominated by conifers, the situation is even worse. In fact, the conifer mortality in Brandenburg is now obvious," says Lukas Kleine, doctoral student in Tetzlaff's team.

and more on:
https://www.eurekalert.org/pub_releases/2020-07/fb-wit071720.php
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The Walrus

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Re: General Drought Stuff
« Reply #256 on: July 21, 2020, 05:25:07 PM »
"We show that the water savings that plants experience under high CO2 conditions compensate for much of the effect of warmer temperatures, keeping the amount of water on land, on average, higher than we would predict with common drought metrics, and with a different spatial pattern. The implications of plants needing less water under high CO2 reaches beyond drought prediction to the assessment of climate change impacts on agriculture, water resources, wildfire risk, and vegetation dynamics."

https://www.pnas.org/content/113/36/10019

John Batteen

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Re: General Drought Stuff
« Reply #257 on: July 22, 2020, 01:58:07 AM »
Fascinating, Walrus.  That ties right in with my topic a couple months ago about the 100th meridian aridity divider.  I believe we're seeing it in action already.  Thanks for sharing!