B1 and B2 DESCRIPTION:
Global field of long-term average annual climate moisture index (CMI, Willmott and Feddema, 1992) computed using the ratio of annual precipitation (P) to annual potential evapotranspiration, (PET), specifically CMI = (P / PET) –1 when P < PET and CMI = 1- (PET / P) when P ≥ PET. The indicator ranges from –1 to +1, with wet climates showing positive CMI, and dry climates negative CMI. PET was estimated using the physically-based function of Shuttleworth and Wallace (1985), which is a modification of the standard Penman-Monteith PET equation. Long-term average precipitation was computed from Mitchell et al. (2003). Coefficient of variability (CV) is computed as the annual standard deviation divided by long-term annual mean.
(B1) cmi_annual_mean.asc = long-term annual average climate moisture index (unitless) computed from annual CMI fields. Primary source: Wilmott and Feddema (1992).
(B2) cmi_annual_cv.asc = long-term annual average climate moisture coefficient of variability (unitless) computed from annual CMI fields. Primary source: Wilmott and Feddema (1992).
Fekete, B. M., C. J. Vorosmarty, and W. Grabs. 2002. High-resolution fields of global runoff combining river discharge and simulated water balances, Global Biogeochemical Cycles, 16 (3): 15-1 to 15-10.
Mitchell, T.D., Carter, T.R., Jones, P.D., Hulme,M., New, M., 2004. A
comprehensive set of high resolution grids of monthly climate for
Shuttleworth, W. J. and J. S. Wallace. 1985. Evaporation from sparse crops: an energy combination theory, Quarterly J. R. Meteorol. Soc., 111: 839-855.
Willmott, C.J., and J.J. Feddema. 1992. A more rational climatic moisture index. Prof. Geographer 44: 84-87.