## 3 Results and Discussion
More evidence that agriculture did not recover as quickly in South Texas as it did in Houston. The situation for the years 2010 to 2011 again, like Houston, illustrate the severity of the drought with predominance of bare soil expansion. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Land Use/Cover** & **2009 (H)** & **2009 (ST)** & **2010 (H)** & **2010 (ST)** & **2011 (H)** & **2011 (ST)** \\ \hline Urban & 10.6 & 10.5 & 11.3 & 5.2 & 11.4 & 18.4 \\ Rocks/soil & 7.2 & 4.0 & 5.2 & 7.5 & 14.1 & 28.4 \\ Agriculture & 23.8 & 71.0 & 23.5 & 71.6 & 25.4 & 44.0 \\ Forest & 57.0 & 14.0 & 58.8 & 15.0 & 47.9 & 8.6 \\ Water & 1.3 & 0.6 & 1.3 & 0.7 & 1.3 & 0.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Land use/cover changes (%) from supervised classification: Houston (H), South Texas (ST). Figure 4: Image differences for 2009 and 2010, and 2010 and 2011 using NDVI, BI, and NDMI for (**a**) Houston, (**b**) South Texas. Figure 5: **(a)** Change vector magnitude for NDVI and NDMI for Houston site; **(b)** change vector direction for NDVI and NDMI for Houston site. Figure 6: (a) Change vector magnitude for NDVI and NDMI for South Texas site. (b) Change vector direction for NDVI and NDMI for South Texas site. Figure 7: (**a**) Change vector magnitude with threshold for NDVI and NDMI for Houston site. (**b**) Change vector direction with threshold for NDVI and NDMI for Houston site. Figure 8: (**a**) Change vector magnitude with threshold for NDVI and NDMI for South Texas site. (**b**) Change vector direction with threshold for NDVI and NDMI for South Texas site. Most pixels are unchanged, both for 2009 to 2010 (almost 82% for Houston and over 78% for South Texas) and for 2010 to 2011 (over 78% for Houston and over 73% for South Texas) (Table 2). Over the remaining, more pixels represented high level changes; of those slightly more were for the 2010 to 2011 years, indicating a more rapid change to drought conditions than the wetting period of the previous year. When examining individual land use/cover classes, the majority of high level changes on the Houston site were pixels representing agriculture or forest; precisely the ones most likely to be affected by chlorophyll increase or bare soil expansion in times of precipitation or sustained ariity. For South Texas, agriculture changed the most within the high threshold as chlorophyll increase accounted for around 60% of the total landscape. However, in the years 2010 to 2011, agriculture accounted for 90% of high-level change, this time as a result of bare soil expansion. Image differences using TCT brightness, greenness, and wetness are consistent with the semi-drought conditions present in 2009, improving to average wet conditions in 2010, and then the exceptionally dry year of 2011 for Houston (Figure 9a). Brightness however, is somewhat of an outlier as for 2009-2010, large areas of the scene appear to be increasing in brightness while in 2010-2011, areas are decreasing in brightness. In comparison many parts of the South Texas site indicate drying conditions for 2009-2010 period (again, because the 2010 image was taken in August), and then deteriorating conditions towards drought in 2011 (Figure 9b). The two study sites demonstrate variations in change vector magnitude. The Houston site experienced low-level changes across the majority of its area-other than patches in the south and south-west (Figure 10a). However, at the South Texas site higher-level changes are apparent throughout the whole area, especially for the 2010 to 2011 years (Figure 11a). In terms of change direction using TCT, it is difficult to discern which change class dominates the 2009 to 2010 years across Houston (Figure 10b). However, for the 2010 to 2011 years there is a noticeable dominance of the yellow class, particularly on the west side; this class corresponds with increases in brightness (B), combined with a decrease in both greenness (G) and wetness (W).