Monitoring Agricultural Drought in Poland - Monitoring and Predicting Agricultural Drought: A Global Study - page 175

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Figure 13.4 Map of distribution of drought conditions at the end of June 1992.

indices, vegetation condition index (VCI), normalized difference vegeta-
tion index (NDVI), and temperature condition index (TCI), were used to
monitor crop conditions and droughts in Poland. Chapter 6 provides a
detailed description of derivation of these indices. Indices were computed
for every week for 1985-98. During this period of 14 years, crop yields
varied significantly and so did the indices. The following yield models were
developed by regressing the deviations in yields and indices.
Analysis of TCI and VCI in different years revealed that the most im-
portant for crop yield assessment are the TCI values in weeks 16 and 22
and the VCI values in week 25. Based on these findings the model was
developed using 1985-97 data, which relates yield deviation from mean
( Y / Y mean ) with TCI and VCI values as described below:
Y / Y mean = 103 . 492 − 0 . 273 ( TCI 16 )

0 . 004 ( VCI 25 ) [13.1]
The above model was used to make yield predictions for 1998 for
Poland. The yield predictions were issued four weeks before harvest. The
results were compared with yield estimates produced with the use of con-
ventional methods by the Central Statistical Office. The mean error of

+ 0 . 214 ( TCI 22 ) +