Functional differences between summer and winter season rain assessed with MODIS derived phenology in a semi-arid region

Authors: JENERETTE, G. - UNIVERSITY OF ARIZONA; Scott, Russell - Russ; HUETE, A. - UNIVERSITY OF ARIZONA

Submitted to: Journal of Vegetation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2009
Publication Date: 1/20/2010
Citation: Jenerette, G.D., Scott, R.L., Huete, A.R. 2010. Functional differences between summer and winter season rain assessed with MODIS derived phenology in a semi-arid region. Journal of Vegetation Science. 21:16-30.

Interpretive Summary: The dynamics of vegetation greenness, including its timing, peak, and total growth exhibit substantial complexity in both space and time. This variation directly affects individual plants, vegetation communities and ecosystem functioning and is implicated as a critical biological response to global changes. The authors’ objective in this paper was to evaluate hypothesized functional relationships between precipitation and plant/ecosystem greenness in the northern Sonoran Desert using remotely-observed greenness patterns. Both summer and winter peak greenness responded positively to precipitation; however, the timing of greenness, its interactions with prior season precipitation, and distribution in space and time varied substantially. These complex analyses of greenness-precipitation relationships help elucidate the complexity in regional vegetation dynamics for a region which has two distinct rainfall seasons.

Technical Abstract: Our objective was to evaluate the interactions between precipitation and phenology across a range of spatial and temporal scales for both the summer and winter rain seasons in southern Arizona using remotely observed phenological patterns and monthly estimates of precipitation. We compared phenological variation between 39 distinct 625 km2 landscapes distributed in northern Sonoran desert between 2000-2007. Regression analyses were used to identify relationships between mean landscape phenology dynamics in response to precipitation variability. Vegetation patterns were clearly coupled with precipitation variability. Disaggregating vegetation into phenological variation spanning value, timing, and integrated components revealed substantial complexity in precipitation-phenological relationships. Both summer and winter peak vegetation responded positively to precipitation; however, the timing of phenological events, interactions with prior season precipitation, and spatio-temporal variability varied substantially. Surprisingly, summer maximum growth was negatively affected by winter season precipitation. Summer and winter precipitation induces distinct phenological responses. While both seasons show increases peak greenness and peak growth, the timing of peak growth was advanced with more rain in winter while the timing of peak greenness was advanced with more rain in summer. Prior season precipitation was more important for summery phenology than winter phenology. The spatial variation between summer and winter phenology were similar in magnitude and both responded similarly precipitation with more precipitation advancing the start of the growing season and lengthening the growing season length. The larger scale spatial and temporal variation showed strong differences in precipitation, with summer precipitation having larger regional but smaller interannual variation than winter precipitation. However, the magnitudes of phenological spatial variability in these two seasons were similar. Multiple-scale analyses of phenology-precipitation relationships help elucidate the complexity in regional vegetation dynamics in these bimodal precipitation regions.