Lake Chad Total Surface Water Area as Derived from Land Surface Temperature and Radar Remote Sensing Data

Abstract

Lake Chad, located in the middle of the African Sahel belt, underwent dramatic decreases in the 1970s and 1980s leaving less than ten percent of its 1960s surface water extent as open water. In this paper, we present an extended record (dry seasons 1988-2016) of the total surface water area of the lake (including both open water and flooded vegetation) derived using Land Surface Temperature (LST) data (dry seasons [2000][2001][2002][2003][2004][2005][2006][2007][2008][2009][2010][2011][2012][2013][2014][2015][2016] from the NASA Terra MODIS sensor and EUMETSAT Meteosat-based LST measurements (dry seasons 1988-2001) from an earlier study. We also examine the total surface water area for Lake Chad using radar data (dry seasons 2015-2016) from the ESA Sentinel-1a mission. For the limited number of radar data sets available to us (18 data sets), we find on average a close match between the estimates from these data and the corresponding estimates from LST, though we find spatial differences in the estimates using the two types of data. We use these spatial differences to adjust the record (dry seasons 2000-2016) from MODIS LST. Then we use the adjusted record to remove the bias of the existing LST record (dry seasons 1988-2001) derived from Meteosat measurements and combine the two records. From this composite, extended record, we plot the total surface water area of the lake for the dry seasons of 1988-1989 through 2016-2017. We find for the dry seasons of 1988-1989 to 2016-2017 that the maximum total surface water area of the lake was approximately 16,800 sq. km (February and May, 2000), the minimum total surface water area of the lake was approximately 6400 sq. km (November, 1990), and the average was approximately 12,700 sq. km. Further, we find the total surface water area of the lake to be highly variable during this period, with an average rate of increase of approximately 143 km 2 per year.

The Lake Chad hydrology under current climate change

“…Lake Chad's surface water extent was maximum in 2001-2002 (~5800 km 2 ), then it continuously declined to its minimum in 2010 (~1800 km 2 ) before starting to slowly increase again in the following years. Compared to previous studies, Lake Chad's surface water extent are lower than what was already reported 6,12 where the minimum, maximum and average of its surface water extent in dry seasons from 1988-1989 to 2016-2017 were estimated at 12,700 km 2 , 16,800 km 2 and 6,400 km 2 , respectively. The large difference mainly comes from the way to define surface water.…”

“…If we assumed that all vegetation area of Lake Chad is also inundation, then the total surface water extent in October 2013 was 12,800 km 2 , in the range of previous results, e.g. 14,000 km 2 , reported in others studies 10,12 . Similarly, recent studies 11,13 reported the minimum, maximum and average size of Lake Chad for the 2003-2016 period were only 1242 km 2 , 2231 km 2 and 1694 km 2 , respectively.…”

“…However, these estimates were usually based on partial observations and thus provided incomplete information and increased misunderstanding of the Lake Chad hydrological cycle. Other studies only investigated the southern pool of the lake 11 , during some months in a year 12 , or only focused on groundwater 13 . Only two studies investigated in details the seasonal variations of the Lake Chad, but focusing on the previous decades, the 1980s and the 1990s 6,14 .…”

Seasonal and Interannual Patterns and Controls of Hydrological Fluxes in an Amazon Floodplain Lake With a Surface‐Subsurface Process Model

“…Acoustic Doppler current profiles allow integrated measurements of discharge. Remote sensing data and approaches can also be utilized as inputs to hydrological models of Amazon floodplain lakes, e.g., (Alsdorf et al, 2000;Hamilton et al, 2002;Hess et al, 2003;Policelli et al, 2018;Rudorff et al, 2014b). Advances in modeling and measuring hydrodynamic processes permit mixing to be examined mechanistically (Augusto-Silva et al, 2018;MacIntyre et al, 2014;Tedford et al, 2014;Vidal et al, 2013).…”

Application of GRACE to the estimation of groundwater storage change in a data‐poor region: A case study of Ngadda catchment in the Lake Chad Basin

“…It has been known that the lake area has declined to less than 2,000km 2 in the 1990s (Grove, ). Recent studies by Leblanc, Lemoalle, Bader, Tweed, and Mofor () and Policelli, Hubbard, Jung, Zaitchik, and Ichoku () though found that the measurement of lake water including open water and flooded vegetation would lead to significantly greater total water area of the lake in the late 1980s through 2016 than had been suggested before. Many studies explain human and natural impacts on the water resources of Lake Chad as well, such as two severe droughts that occurred in the periods 1972–1974 and 1983–1987 (Kimmage & Adams, ), desertification (IPCC, ), overgrazing (FAO, ), irrigation activities (Isiorho & Njock‐Libii, ), vegetation removal and modification (Keith & Plowers, ), and deforestation (Neiland & Verinumbe, ), along with population increase (UN Population Division, ).…”