Leaderboard

On February 7, 2017, the twentieth and final inclination (Delta-I) maneuver of Landsat 7 took place. (Delta-I maneuvers keep the spacecraft in the correct orbital position to ensure it maintains its 10:00 am ± 15 minutes mean local time (MLT) equatorial crossing.) Landsat 7 reached its peak outermost inclination boundary of 10:14:58 MLT on August 11, 2017. Landsat 7 is now drifting in its inclination and will fall back to 09:15 am MLT by July 2021. The chart below illustrates the inclination trend from June 2014 to June 2026. The USGS and NASA are planning for Landsat 7 to remain on-station and fulfilling its current science mission until Landsat 9 completes its launch (scheduled for September 16, 2021), on-orbit checkout, and commissioning. Sometime after Landsat 9 is nominally acquiring science mission data, Landsat 7 will exit the constellation and lower its orbit by 8 km to prepare for servicing by NASA’s On-Orbit Servicing, Assembly, and Manufacturing-1 (OSAM-1) mission. The mission - the first of its kind in low Earth orbit - will provide Landsat 7 with the needed fuel for a successful decommissioning. source: https://www.usgs.gov/core-science-systems/nli/landsat/landsat-7?qt-science_support_page_related_con=0#qt-science_support_page_related_con

Many of Africa’s agricultural endeavors have long been tied to whims of the weather. When it rains, a country’s gross domestic product might soar. When it doesn’t rain, economies suffer. The reliance has been driven in part by the perception that dry, arid Africa has limited water resources. But a new study, years in the making, shows a different reality. As one South African scientist recently noted, if all the rainfall stopped today and for the next 100 years in Africa, there would still be plenty of water stored underneath the continent’s surface, it just wouldn’t be evenly distributed. That’s why maps are essential in showing which aquifers are vulnerable to rainfall variability. “You can imagine the possibilities,” said hydrologist Seifu Kebede Gurmessa from the University of KwaZulu-Natal in South Africa and coauthor of the study. The study, released in February, uses maps from a geographic information system (GIS) analysis to show water replenishment across the continent. It turns out that the vast majority of Africa’s countries either have high water storage or high levels of groundwater replenishment. Five countries have both. Five have neither. “We say we are prisoners of the rainfall,” Gurmessa said of Africa’s dependence on the resource for agriculture, one of the continent’s largest economic outputs. Little groundwater, proportionately, is used for irrigation currently. “How can we break that imprisonment of seasonality in the rainfall?” Groundwater use could be a buffer for the stark seasonal swings. Important Water Discoveries The report, Mapping Groundwater Recharge in Africa from Ground Observations and Implications for Water Security, was led by the British Geological Survey (BGS) and is a sequel to another of the BGS’s groundbreaking studies. Using a geographic information system to aggregate information and perform spatial analysis, the report’s authors brought old data into the present by incorporating factors that impact groundwater recharge including climate, amount of rainfall, the number of wet days in a year, land cover, vegetation health, and soil type. Nearly a decade ago, the team of international scientists created a map that showed Africa actually had a rather large volume of water hidden and stored underneath the surface. However, the researchers behind the science-shifting report and, later, the BGS’s Africa Groundwater Atlas knew that that was only part of the continent’s water story. Groundwater, like a bank account, depends on regular deposits to balance withdrawals. Once again, results of the latest research were promising. The study’s authors were able to clearly map, for the first time, which countries had sustainable resources and which ones didn’t. The countries were separated into four color-coded categories: low storage/low recharge, high storage/low recharge, low storage/high recharge, and high storage/high recharge. “That map is really key in proposing what you can do in different countries,” Gurmessa said. Click on the image to see a larger map of groundwater recharge and storage in African countries. Most countries had one or the other—high storage or high recharge. Alan MacDonald, the study’s leader and a hydrogeologist with the British Geological Survey, has called it a happy symmetry. “Still,” he said, “so many people in Africa don’t have any access to safe water.” He and the others involved hope their comprehensive research starts a conversation—just like their first report did in 2012—about what’s possible and what isn’t. For instance, what kind of access to water should be installed in a village if groundwater is plentiful but rainfall is scarce? While none of the scientists involved contemplates a pumping free-for-all that could deplete groundwater, the report does suggest the continent has been faring better than might have been expected in maintaining a healthy water supply. “It’s not all doom and gloom. It’s not all bad. In some areas, there is potential for groundwater to provide safe water supplies for many more people than currently have them,” said Kirsty Upton, who oversees BGS’s Africa Groundwater Atlas. As the report itself states, “With increasing calls to draw from groundwater storage in order to stimulate economic growth and improve food security in Africa, a more nuanced approach to water security is necessary.” Making Sustainable Plans The team’s 2012 countrywide study of the continent’s groundwater conditions—a first of its kind that attracted media attention—led government ministers to hang the study’s maps from office walls. The work also encouraged funding to help 50 Africa-based partners to create a continental groundwater atlas, with data downloaded thousands of times by nongovernmental organizations, governments, students, and researchers. The study’s research and data were also the foundation for the latest groundwater recharge report, which reveals how sustainable the water supply is. “That was the next stage for us,” MacDonald said. Ten scientists including MacDonald—five in Africa and the others from around the world—promptly got to work, pouring over 320 existing studies to find the most reliable information as well as common themes. They were about to publish in 2017 until MacDonald, noticing that some of the geolocation data for the original reference studies was off, started from the very beginning again to reanalyze the information. “You want to get this right,” he said considering the importance of the data and how far its reach may be. He recalled a moment, shortly after the 2012 study on groundwater was released, when he met two French mountaineers who had a copy of the daily newspaper Le Monde. “And there was a picture of my maps,” he said. He likened the maps, including the most recent study on replenishment, to a conversation starter. Click on the image to see a larger map of African rainfall and groundwater recharge. “If you do get a map that people are really going to look at and use, you want to make sure that you’re giving them information that is useful to them and is a gateway to more information, and not misleading people,” MacDonald said. The researchers continue to be curious too, looking at additional facets. They’re already developing their next study, looking at the quality—primarily the salinity—of Africa’s groundwater. A Promising Future For the most recent study, researchers focused on long-term average groundwater recharge rates across Africa from 1970 to 2019. They used 134 existing studies deemed the most reliable, winnowing the total down from 320 and factoring in climate and terrestrial parameters to scale for the entire continent. The process wasn’t quick, easy, or highly technical. In other projects, MacDonald said, he has used data from the National Aeronautics and Space Administration (NASA) GRACE satellite, which measures water storage changes from space, averaging over a large area (400 x 400 km) to indicate whether an area’s water has been recently depleted. “But it only gets you so far,” he said, and this time the researchers needed to look in much more detail to understand water renewability on the continent. “It was sheer old-fashioned grunt work.” He and the others went through old files and maps, some found on dusty shelves. The result of this investigation—funded primarily by the UPGro research program, whose mission is Unlocking the Potential of Groundwater for the Poor—was published in Environmental Research Letters in February. “It is really a good time to be a groundwater expert in this decade in Africa,” Gurmessa said. “The future also looks more promising.” Access to and availability of water can affect a whole host of issues, ranging from school attendance to conflict that comes from agriculture workers migrating from one rural area to another, not to mention overall human health. Water is tied to everything in one’s life, he pointed out. source: https://www.esri.com/about/newsroom/blog/africa-groundwater-mapping/

Classification of precipitation change regimes based on changes in the precipitation mean state and variability. Shading indicates the ratio of change in precipitation variability and mean precipitation. Climate models predict that rainfall variability over wet regions globally will be greatly enhanced by global warming, causing wide swings between dry and wet conditions, according to a joint study by the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences (CAS) and the Met Office, the UK's national meteorological service. This study was published in Science Advances on July 28 2021. Increased rainfall leads to floods, less rainfall to drought. Researchers realized decades ago that global warming drives increased rainfall on average. How this increase is delivered in time matters enormously. A 2 to 3 percent increase of annual precipitation uniformly spreading across the year does not mean much, but if it falls in a week or a day, it will cause havoc. Using large ensembles of state-of-the-art climate model simulations, this study highlights the increase in rainfall variability across a range of time scales from daily to multiyear. Scientists have found that in a future warming world, climatologically wet regions (including the tropics, monsoon regions and mid- to high-latitudes) will not only get wetter on average, but also swing widely between wet and dry conditions. "As climate warms, climatologically wet regions will generally get wetter and dry regions get drier. Such a global pattern of mean rainfall change is often described as 'wet-get-wetter'. By analogy, the global pattern of rainfall variability change features a 'wet-get-more variable' paradigm. Moreover, the global mean increase in rainfall variability is more than twice as fast as the increase in mean rainfall in a percentage sense," said Zhou Tianjun, corresponding author of the study. Zhou is a senior scientist at IAP. He is also a professor at the University of Chinese Academy of Sciences. The enhanced rainfall variability, to a first order, is due to increased water vapor in the air as climate warms, but is partly offset by the weakening circulation variability. The latter dominates regional patterns of change in rainfall variability. By considering changes in both the mean state and variability of precipitation, the research provides a new perspective for interpreting future precipitation change regimes. "Around two-thirds of land will face a 'wetter and more variable' hydroclimate, while the remaining land regions are projected to become 'drier but more variable' or 'drier and less variable'. This classification of different precipitation change regimes is valuable for regional adaptation planning," said Zhang Wenxia, lead author of the study. "The globally amplified rainfall variability manifests the fact that global warming is making our climate more uneven—more extreme in both wet and dry conditions, with wider and probably more rapid transitions between them," said Kalli Furtado, expert scientist at the Met Office and second author of the study. "The more variable rainfall events could further translate into impacts on crop yields and river flows, challenging the existing climate resilience of infrastructures, human society and ecosystems. This makes climate change adaptation more difficult." source: https://phys.org/news/2021-07-rainfall-increasingly-variable-climate.html