REGIONAL HYDROLOGIC RESPONSE OF LOBLOLLY PINE TO AIR TEMPERATURE AND PRECIPITATION CHANGES¹

Abstract

Large deviations in average annual air temperatures and total annual precipitation were observed across the southern United States during the last 50 years, and these fluctuations could become even larger during the next century. We used PnET‐IIS, a monthly time‐step forest process model that uses soil, vegetation, and climate inputs to assess the influence of changing climate on southern U.S. pine forest water use. After model predictions of historic drainage were validated, the potential influences of climate change on loblolly pine forest water use was assessed across the region using historic (1951 to 1984) monthly precipitation and air temperature which were modified by two general circulation models (GCMs). The GCMs predicted a 3.2°C to 7.2°C increase in average monthly air temperature, a ‐24 percent to + 31 percent change in monthly precipitation and a ‐1 percent to + 3 percent change in annual precipitation. As a comparison to the GCMs, a minimum climate change scenario using a constant 2°C increase in monthly air temperature and a 20 percent increase in monthly precipitation was run in conjunction with historic climate data. Predicted changes in forest water drainage were highly dependent on the GCM used. PnET‐IIS predicted that along the northern range of loblolly pine, water yield would decrease with increasing leaf area, total evapotranspiration and soil water stress. However, across most of the southern U.S., PnET‐IIS predicted decreased leaf area, total evapotranspiration, and soil water stress with an associated increase in water yield. Depending on the GCM and geographic location, predicted leaf area decreased to a point which would no longer sustain loblolly pine forests, and thus indicated a decrease in the southern most range of the species within the region. These results should be evaluated in relation to other changing environmental factors (i.e., CO2 and O3) which are not present in the current model.

Streamflow Response to Climate and Landuse Changes in a Coastal Watershed in North Carolina

“…Climate change and variability have both direct and indirect effects on the hydrologic cycle at multiple scales by altering the physical and biological processes of ecosystems (McNulty et al, 1997). Climate change directly affects precipitation amount and intensity and potential evapotranspiration (Calder et al, 1995).…”

“…McNulty et al (1997) and Sun et al (2000) conducted several hydrologic impact studies at the watershed to regional scale across the southern U.S., in which 55% of the land mass is covered by forests, using the forest ecosystem model PnET. They found that climate warming would increase forest evapotranspiration as forest growth increases, but overall water yield was expected to follow the trends of projected precipitation patterns.…”

“…Simulation models are available to begin to address climate change issues in the southeast at the watershed to regional scales. Climate change impact studies have been conducted at the national scale (Wolock and McCabe, 1999;Rosenberg et al, 2003), across the southeastern region (McNulty et al, 1997;Sun et al, 2008), and for a large watershed scale (Nash and Gleick, 1991). For example, Stone et al (2001) used the SWAT model (Arnold et al, 1998), coupled with a regional climate model to examine how doubling atmospheric CO 2 affects water yield for the Missouri River basin.…”

Spatiotemporal Characteristics of Reference Evapotranspiration and Its Sensitivity Coefficients to Climate Factors in Huang-Huai-Hai Plain, China

“…ET 0 is an integrated climate parameter that gives a measure of the evaporation demand of the air. Several researches have pointed out that ET 0 is expected to increase with temperature rise (McNulty et al 1997;Goyal 2004). However, decreasing trends of ET 0 were found in some areas of China (Thomas 2000;Shenbin et al 2006;Wang et al 2007), India (Chattopadhyay and Hulme 1997), USA (Hobbins et al 2004), and Australia (Roderick and Farquhar 2004).…”

Future directions for hydropedology: quantifying impacts of global change on land use

“…Few studies have been performed to examine climate change impacts for the Southeastern Region. McNulty et al (1997) and Sun et al (2000) studied change-climate impacts on forest hydrology at the watershed to regional scale across the Southern US using the ecosystem model PnET. They found that climate warming would increase forest evapotranspiration as forest growth increases, but overall water yield was expected to follow the trends of projected precipitation patterns.…”