Characteristic Features of Heavy Rainfall over Gujarat and Rajasthan States of India due to Very Severe Cyclonic Storm Phet over the Arabian Sea (31 May to 07 June 2010) - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 412

for the observed values greater than 30 mm/day. Inter-comparison of
heavy rainfall of more than 6.5 cm per day reported by stations with TRMM
daily rainfall estimate done and shown in Fig. 5d shows positive correlation
(nearly 0.6).
Figure 6 shows the inter-comparison of observed rainfall and TRMM 3B42
daily rainfall over Rajasthan on 8 th June 2010. From Fig. 6a and Fig. 6b it is
clearly seen that the spatial distribution of rainfall is well captured by TRMM
3B42 daily rainfall data whereas the intensity is underestimated as compared
to the observed daily rainfall data. The scatter-plot (Fig. 6c) shows positive
correlation (nearly 0.5) between gauge daily rainfall and TRMM 3B42-V6
estimates. The low slope value suggests that the higher rainfall values are
underestimated. The scattered is more for the observed values greater than 30
mm/day. Inter comparison of heavy rainfall of more than 6.5 cm per day reported
by stations with TRMM daily rainfall estimate done and shown in Fig. 6d
shows positive correlation between actual rainfall and TRMM estimates.
Comparison of results indicates that the performance of TRMM estimate
varies from day to day and region to region. The heavy rainfall (>65 mm) is
always underestimated by TRMM estimate for both Gujarat and Rajasthan
states. However for moderate rain (<30 mm) there is positive strong correlation
over both the states . The correlation between actual rainfall and TRMM
estimates is higher over Rajasthan (predominantly over desert land) than over
Gujarat. It indicates dominant role of land surface processes on occurrence of
heavy rainfall in association with a TC over the region during onset phase of
monsoon (Xue et al., 2004). According to Xue et al. (2004), exchanges of
water and energy between the vegetation and the atmosphere play an important
role in East Asian and West African monsoon development and are among the
most important mechanisms governing the development of the monsoon. Based
on a general circulation model (GCM) coupled with two different land surface
parameterizations, with and without explicit vegetation representations, referred
to as the GCM/vegetation and the GCM/soil, two land surface models produced
similar results at the planetary scale but substantial differences at regional scales,
especially in the monsoon regions and some of the large continental areas. In
the simulation with GCM/soil, the East Asian summer monsoon moisture
transport and precipitation were too strong in the pre-monsoon season. The
two land surface representations produced different longitudinal and latitudinal
sensible heat gradients at the surface that, in turn, influenced the low-level
temperature and pressure gradients, wind flow (through geostrophic balance),
and moisture transport. The latitudinal heating gradient may contribute to the
clockwise and counterclockwise turning of the low-level wind. Under unstable
atmospheric conditions, not only low-frequency mean forcing from the land
surface, such as monthly mean albedo, but also the perturbation processes of
vegetation are important to the monsoon evolution, affecting its intensity, the
spatial distribution of precipitation.