Wetlands inform how climate extremes influence surface water expansion and contraction

Abstract

Abstract. Effective monitoring and prediction of flood and drought events requires an improved understanding of how and why surface water expansion and contraction in response to climate varies across space. This paper sought to (1) quantify how interannual patterns of surface water expansion and contraction vary spatially across the Prairie Pothole Region (PPR) and adjacent Northern Prairie (NP) in the United States, and (2) explore how landscape characteristics influence the relationship between climate inputs and surface water dynamics. Due to differences in glacial history, the PPR and NP show distinct patterns in regards to drainage development and wetland density, together providing a diversity of conditions to examine surface water dynamics. We used Landsat imagery to characterize variability in surface water extent across 11 Landsat path/rows representing the PPR and NP (images spanned 1985-2015). The PPR not only experienced a 2.6-fold greater surface water extent under median conditions relative to the NP, but also showed a 3.4-fold greater change in surface water extent between drought and deluge conditions. The relationship between surface water extent and accumulated water availability (precipitation minus potential evapotranspiration) was quantified per watershed and statistically related to variables representing hydrology-related landscape characteristics (e.g., infiltration capacity, surface storage capacity, stream density). To investigate the influence stream connectivity has on the rate at which surface water leaves a given location, we modeled stream-connected and stream-disconnected surface water separately. Stream-connected surface water showed a greater expansion with wetter climatic conditions in landscapes with greater total wetland area, but lower total wetland density. Disconnected surface water showed a greater expansion with wetter climatic conditions in landscapes with higher wetland density, lower infiltration and less anthropogenic drainage. From these findings, we can expect that shifts in precipitation and evaporative demand will have uneven effects on surface water quantity. Accurate predictions regarding the effect of climate change on surface water quantity will require consideration of hydrology-related landscape characteristics including wetland storage and arrangement.

A National Assessment of Wetland Status and Trends for Canada’s Forested Ecosystems Using 33 Years of Earth Observation Satellite Data

“…Major droughts affecting much of the southern part of our study area occurred in 2000, 2001, and 2015 [52], and correspond with the years in which we found the minimum wetland extent in the majority of ecozones. Other studies have likewise reported reductions in wetland coverage during extreme drought years, especially in dry regions [4]; and an understanding of how extreme drought years have historically affected wetland extent provides valuable insight to the potential effects of future climate change. Our finding that maximum wetland extent occurred from 2012 to 2016 in all northern and mountainous ecozones, but not the southern parts of the study area or the maritime zones, implies melting ice, snow, and permafrost are contributing to increased water and wetland expansion in recent years.…”

“…1 All Wetland-Occurring Area: Area of pixels that were classified as wetland at least once over the entire 33 years, i.e., sum of all the five temporal states; 2 Always: Area that was classified as wetland for ≥13 years in both epochs (before and after 2000); 3 Is Now: Area that was classified as wetland for <13 years in the 1st epoch (before 2000) and ≥13 years in the 2nd epoch (after 2000); 4 Used-to-Be: Area that was classified as wetland for ≥13 years in the 1st epoch (before 2000) and for <13 years in the 2nd epoch (after 2000); 5 Sometimes: Area that was not in the previous three temporal states, but was classified as wetland for ≥13 years throughout the two epochs; 6 Rarely: Area that was classified as wetland for <13 years, but at least once during the entire 33 years. 1 All Wetland-Occurring Area: Area of pixels that were classified as wetland at least once over the entire 33 years, i.e., sum of all the five temporal states; 2 Always: Area that was classified as wetland for ≥13 years in both epochs (before and after 2000); 3 Is Now: Area that was classified as wetland for <13 years in the 1st epoch (before 2000) and ≥13 years in the 2nd epoch (after 2000); 4 Used-to-Be: Area that was classified as wetland for ≥13 years in the 1st epoch (before 2000) and for <13 years in the 2nd epoch (after 2000); 5 Sometimes: Area that was not in the previous three temporal states, but was classified as wetland for ≥13 years throughout the two epochs; 6 Rarely: Area that was classified as wetland for <13 years, but at least once during the entire 33 years. 1 All Wetland-Occurring Area: Area of pixels that were classified as wetland at least once over the entire 33 years, i.e., sum of all the five temporal states; 2 Always: Area that was classified as wetland for ≥13 years in both epochs (before and after 2000); 3 Is Now: Area that was classified as wetland for <13 years in the 1st epoch (before 2000) and ≥13 years in the 2nd epoch (after 2000); 4 Used-to-Be: Area that was classified as wetland for ≥13 years in the 1st epoch (before 2000) and for <13 years in the 2nd epoch (after 2000); 5 Sometimes: Area that was not in the previous three temporal states, but was classified as wetland for ≥13 years throughout the two epochs; 6 Rarely: Area that was classified as wetland for <13 years, but at least once during the entire 33 years.…”

“…1 All Wetland-Occurring Area: Area of pixels that were classified as wetland at least once over the entire 33 years, i.e., sum of all the five temporal states; 2 Always: Area that was classified as wetland for ≥13 years in both epochs (before and after 2000); 3 Is Now: Area that was classified as wetland for <13 years in the 1st epoch (before 2000) and ≥13 years in the 2nd epoch (after 2000); 4 Used-to-Be: Area that was classified as wetland for ≥13 years in the 1st epoch (before 2000) and for <13 years in the 2nd epoch (after 2000); 5 Sometimes: Area that was not in the previous three temporal states, but was classified as wetland for ≥13 years throughout the two epochs; 6 Rarely: Area that was classified as wetland for <13 years, but at least once during the entire 33 years. 1 All Wetland-Occurring Area: Area of pixels that were classified as wetland at least once over the entire 33 years, i.e., sum of all the five temporal states; 2 Always: Area that was classified as wetland for ≥13 years in both epochs (before and after 2000); 3 Is Now: Area that was classified as wetland for <13 years in the 1st epoch (before 2000) and ≥13 years in the 2nd epoch (after 2000); 4 Used-to-Be: Area that was classified as wetland for ≥13 years in the 1st epoch (before 2000) and for <13 years in the 2nd epoch (after 2000); 5 Sometimes: Area that was not in the previous three temporal states, but was classified as wetland for ≥13 years throughout the two epochs; 6 Rarely: Area that was classified as wetland for <13 years, but at least once during the entire 33 years.…”

“…Wetlands are significant global contributors to the supply of clean, fresh water and they regulate the hydrological cycle to mitigate floods and protect shorelines. Wetlands also store notable amounts of carbon and other nutrients, thus influencing both water and nutrient cycles as well as modulating climate [1][2][3][4]. Wetlands are the transitional areas between terrestrial uplands and deep, open water [5].…”

“…Natural resource exploration and extraction has caused the degradation or loss of wetlands in more remote regions (oil and gas, mining) [10]. Additionally, climate change may substantially alter wetlands across Canada (i.e., stability, growth, or contraction) and is expected to vary regionally [1,4]. Alterations to wetland ecosystems can also result in public safety concerns as well as impacts to infrastructure where wetlands have previously provided natural mechanisms for reducing flooding in some regions [8].…”