Geolocation of Hydrographic Basins

11 Aug 2021

Official designation of the project: Geolocation of hydrographic basins/watersheds in the Northeast region of Brazil

Start date: November 2, 2021
Completion date: March 1, 2022

Detailed description: Northeast Brazil is one of the most densely populated semi-arid regions on the planet. It is located at an equatorial latitude, with greater incidence of solar rays and, therefore, with higher temperatures. Added to this is the fact that the region does not have a large number of great flow rivers that would favor evaporation and consequent precipitation at the local level.

Most of its rivers are intermittent or seasonal, that is, they dry up in certain periods, with the great exception being the São Francisco River, the main water resource in the region. The region's climate is characterized by two well-defined seasons: one dry and the other moderately rainy, the first being often intensified due to climatic phenomena, which leads to long periods of drought, and hence efficient planning and management of water resources become essential.

This need for efficiency in management is a priority in the warmer months, when there are conflicts in the use of water, and also due to factors that accentuate losses by evaporation. At this stage, it is necessary to have accurate geographic information constantly updated, so knowledge of the existence and location of surface water stores can be extremely useful, as well as the estimation of their reserve capacities, which can be calculated through specific algorithms.

The digital processing of images obtained through remote sensing allows a fast and accurate update of the inventory of surface storages. The satellite navigation systems currently available, in turn, allow the integration of various types of information, which provides a huge advantage in emergency situations, in which it is necessary to decide where to supply vehicles to supply the populations, or even for use in aerial firefighting equipment. These geographic information systems provide the user with the locations of the reservoirs closest to their zones of ​​intervention, their metric area and water availability.

LS-Engenharia Geográfica, in collaboration with Daruma Consultoria (SP-Brasil) started in November 2021 a pilot project for the geolocation of artificial reservoirs and small hydrographic basins in the Brazilian semi-arid region. Through digital processing techniques, and using high-resolution satellite images from the European Copernicus Space Program, it was possible to perform the automatic delimitation of reservoirs and hydrographic basins in the region, at specific periods, store this data in a Geographic Information System and make them available later in various digital formats, in global and national cartographic projection systems.

One of the sensors used is the Sentinel-2 MSI, which acquires images with a revisit period of 5 days, thus allowing a quick update of geographic information, essential for planning strategies in places where water reservoirs, in hot seasons, are consumed in a few weeks due to agricultural use, emergency supplies and evaporation phenomena.

Challenges: The use of multispectral images is influenced by several atmospheric phenomena, in this case the cloud cover that characterizes the Northeast of Brazil, so the pre-selection of images must follow strict criteria.

Advantages: Large geographic coverage, short revisit period, identification of objects with a high degree of confidence, algorithms used allow estimating reserve capacity.

Areas of Intervention: Remote Sensing

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