Microclimate Effects Of Wetlands Observation And Modeling,

Relying on the Honghe National Nature Reserve of the Sanjiang Plain, this studyinvestigated the temporal-spatial variations of microclimate effects (i.e., cold-humideffect) in marsh wetland. Temperature and humidity from marsh wetlands andsurrounding farmlands were measured in the field and simulated at regional scale bythe model of Weather Research and Forecasting (WRF).Compared to surrounding farmlands, the temperature was lower and relativehumidity (RH) was higher at three heights (0.5,2and5m) in marsh wetlands duringthe growing season (from June to September). This indicates the cold-humid effect ofmarsh wetland. The cold-humid effect was most significant at0.5cm, and graduallydecreased with the increasing height. During the non-growing season, the mostsignificant cold-humid effect occurred in July. The biggest differences of temperatureand humility between marsh wetland and farmland were found from12:00to14:00based on daily measurements.The daily variations of soil temperatures (0,5and10cm) at marsh wetland andfarmland were similar in July and August, with a sinusoidal change. During a day, thechange range of soil temperature in marsh wetland was less than that in farmland. Atthe same depth, soil temperature in marsh wetland was lower than that in farmland.The simulations from WRF model show that: WRF model provided comparablevalues of temperature and RH at the height of2m from wetland underlying surface insummer sunny day as compared to that measured in the field.During the summer sunny day, air temperature measured at the edge of wetlandwas higher than at the center of wetland, but was lower than that at surroundingfarmland. There was a decreasing trend of air temperature from the edge to the centerof wetland. The marsh wetland represented a significant cold-island effect, withmaximum effect at14:00and gradually decreased during the night, with minimumeffect at22:00. Our study showed that the cold-island effect of marsh wetland couldbe found at the height of200m at6:00, and the height could extend to600m at14:00. The RH of marsh wetland was higher than that in farmland during both thedaytime and nighttime at the height of2m, indicating the 'wet-island effect' inwetland. The value of RH was highest at the center of wetland, followed at the edgeof wetland and lowest at farmland. Similar diurnal variations of RH were determinedin both wetland and farmland. The RH of marsh wetland was higher in the daytimethan that in the nighttime, with the maximum values at2:00and minimum values at14:00. The change range of RH in a day was higher in farmland then that in marshwetland. The difference of RH between wetland and farmland is biggest during thenighttime, whereas lowest at14:00. At both marsh wetland and farmland, the RHvalues decreased with increasing height. Within the range of200m height, RH valuesin marsh wetland were higher than surrounding farmland.