ALOS-2 ScanSAR data was used for examining the effect of precipitation and soil moisture variations on L-band forest backscatter in tropical regions. Multitemporal data spanning from observation cycle 39 to 62 acquired over tropical forests in South America and Africa has been used. Precipitation data provided through JAXA's global rainfall watch was used to examine the temporal change of L-band σ⁰ for forests as well as deforestation areas. The best choice for temporal integration of rainfall prior to the image acquisitions was investigated. The results show that σ⁰_HH values show an average increase smaller 1 dB, whereas σ⁰_HV values can increase by more than 2 dB in dense forests after heavy rain. Our findings also indicate that dense forest and open/moderately dense forests can show quite different rainfall effects. The latter may even exhibit a decrease in both σ⁰_HH and σ⁰_HV after heavy rain due to standing water. Implementations for the ongoing development of an advanced tropical forest monitoring system are discussed.