Estimation of dewfall amount in a typical desert shrub ecosystem.

Estimation of dewfall amount and its interannual variation in arid and semi-arid transitional ecosystems are still limited. Microlysimeter, eddy covariance (EC) method and Penman-Monteith equation were used to calculate the dewfall amount in a desert shrub ecosystem in Yanchi Research Station, Ningxia, Northwest China. The objectives of this study were to explore the accuracy of EC and Penman-Monteith equation in dewfall estimation, to analyze the seasonal and interannual variations of dewfall amount, the contribution of dewfall amount to the water balance of the ecosystem and the influence of rainfall on dewfall. The results indicated that: 1) taking the results observed by microlysimeter as a control, EC method could lead to a substantial underestimation of dewfall amount because of its low energy closure at night, but the Penman-Monteith equation could precisely estimate dewfall amount (R2 = 0.94, P0.05). 2) Dewfall amount during 2012—2014 was estimated by the Penman-Monteith equation. Mean daily dewfall amount (during 2012—2014) was 0.14±0.08 mm, average number of dewfall days was 259 days per year, dewfall amount in the years 2012 to 2014 was 46, 33 and 29 mm, respectively. Dewfall occurred more frequently in summer and autumn. The average annual rainfall amount during 2012—2014 was 301 mm. The average annual dewfall amount accounted for 12% of the average annual rainfall. 3) Rainfall and the dewfall amount on the day after rainfall showed a significant positive relationship (R2=0.81, P0.05). The percentage of ≥20 mm rainfall events accounted for 10%, 5% and 3% of the yearly total rainfall events in the years 2012 to 2014, respectively. Rainfall larger than 20 mm could add more water vapor in the air, thus increasing dewfall amount. Thereafter the percentage of ≥20 mm rainfall events to the yearly total rainfall events would significantly influence the annual dewfall amount. The results prove that dewfall is an important and stable water resource to maintain the function of desert ecosystem system despite of its large interannual differences and relatively small percentage in rainfall.