Date of Graduation

12-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Environmental Dynamics (PhD)

Degree Level

Graduate

Department

Environmental Dynamics

Advisor/Mentor

Tullis, Jason A.

Committee Member

Matlock, Marty D.

Second Committee Member

Aly, Mohamed H.

Third Committee Member

Fernandes, Katia

Keywords

Climate variability; Spatiotemporal dynamics; Water surface areas

Abstract

This study explores the spatiotemporal dynamics of climate variability and water surface area in Lake Nicaragua, one of the largest tropical lakes on Earth. The significance of this study lies in its potential to provide valuable insights into the hydroclimatic patterns and water availability, vital for Nicaragua’s water supply. Monthly and seasonal time series of precipitation, land surface temperature, and evapotranspiration (ET), acquired from the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) and Moderate Resolution Imaging Spectroradiometer (MODIS), were analyzed in Google Earth Engine using a non-parametric Mann-Kendall trend test and Sen's slope. The second aim of this research was to apply the Landsat Dynamic Surface Water Extent (DSWE) for estimating surface water in Lake Nicaragua. From 1982 to 2021, significant spatiotemporal variations in precipitation across the basin were observed. While a slight positive trend of annual precipitation was noted in the northern part of the basin, negative trends with reductions in annual accumulation of up to 35 mm/year were found in the southern part of the lake, near the Nicaragua-Costa Rica border. The spatial distribution of temperature trends from 2001 to 2021 at a monthly scale indicated that most areas within the basin did not exhibit significant changes. During the dry season, the southern part of the basin and the lake surface exhibited a stronger upward temperature trend, while the central and northern parts showed relatively stable or decreasing temperature trends, suggesting an increase in temperatures during the dry season and an opposite trend during the rainy season. ET data, from 2001 to 2021, showed that during the dry season, there was an overall increase in positive ET trend values, particularly from January to March, where 20% to 31% of areas showed significant trends, attributed to increased soil moisture and intercepted rainfall from vegetation. In the application of DSWE, one of the main obstacles was the disruption of the Landsat record over this area, out of a potential 60 composites over the years, only 40 were successful. On average, cloud cover concealed 5% of Lake Nicaragua's surface area within the seasonal composites. The examination of DSWE class dynamics offered valuable insights into the impact of the season on water classification. DSWE classes 0 and 1, signifying "not water" and "high-confidence water," respectively, exhibited remarkable stability during the rainy season. In contrast, DSWE classes 2 and 3, representing "low to moderate confidence water," displayed significant fluctuations in areas among the seasons, indicating that low-confidence water classes are notably affected by decreased precipitation in the dry season. Meanwhile, DSWE class 3, "moderate confidence water," showed a 15% increase in surface areas during the dry season. DSWE class 4, denoting wetlands, unveiled a noteworthy 32% decrease in areas during the dry season. This study examined the changing hydroclimatic patterns and surface water dynamics in the Lake Nicaragua basin and revealed the complex interplay of climate variables and their impact on this unique ecosystem. Understanding these dynamics is indispensable for informed decision-making and sustainable water resource management in the region.

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Available for download on Thursday, February 13, 2025

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