Spatio-temporal analysis of environmental variables to support water resources management

Abstract

Hydrological studies combined with the use of conservation practices are essential for an adequate management of water resources. It is necessary to expand the knowledge about hydrological processes and their seasonal variations, as well as the rainfall patterns of the different hydrographic basins, considering their spatial and temporal distributions. Thus, the objective with this research is to investigate hydrological processes, soil conservation techniques, cultivation conditions and patterns of temporal space variability of water and electrical conductivity available in the semiarid region of Pernambuco, with emphasis on the use of conservationist techniques and cultivation in experimental plots, with the prospect of increasing agricultural resilience and sustainability in the semiarid region. Chapter 1 covers the general and specific introduction, hypotheses and objective and the literature review. Chapter 2 addresses the verification of the accuracy of indirect measurements of the apparent electrical conductivity (ECa) using the EM38®, as well as of physical-hydric parameters of the soil, and their spatial interrelationships. Chapter 3 presents an investigation of the cross variance between soil moisture and soil apparent electrical conductivity (ECa), under different land uses in an alluvial valley in Pernambuco. Chapter 4 presents the investigation of small-scale hydrological processes and the impact of soil conservation techniques in reducing runoff and sediment losses. This study used the textural characterization of the associated transported sediments, using runoff plots with different soil coverings (bare soil, Caatinga, mulch and Palma) under natural rain, in the Caatinga biome of Brazil. Chapter 5 presents the study of the interception process (i.e., water retention and absorption) of rain by different types, sizes and densities of some organic coverings that are commonly found in the Brazilian semiarid region. These results are important for the definition of soil and water conservation practices in these environments. In general, a high covariance between soil moisture and ECa is identified in the fallow area and under cultivation at different depths, under conditions of extreme water scarcity. For alluvial areas, a covariance of soil moisture with ECa is detected, as well as the occurrence of strong spatial dependence. The effect of mulch due to the deciduous characteristics of Caatinga vegetation is important for maintaining soil moisture, contributing to the development and maintenance of plant biomass in riparian forest. The natural cover (Caatinga) produces less runoff and loss of sediment when compared to bare soil and soil conservation practices (mulch and Palma). Adoptions of organic cover dosages from 2 t ha-1 already promote significant retention/absorption, contributing to possible delay in the onset of runoff, increased water infiltration and consequent reduction of water and soil losses.