# Drought Propagation in Brazilian Biomes Revealed by Remote Sensing
## 3 Results
### Drought Propagation Analysis  
The negative anomalous values (z-score \(\leq-1\)) in the drought events, plotted with 3-month moving averages (Figure 4), showed that the anomalies in _TWSA_ lasted longer and had more accentuated values during the 2015 Amazon drought than during the 2010 event. For the vegetation and _LST_ variables, taking out the _GPP_ peak in 2016, the droughts show reduced anomaly values for _EVI_ (reaching a z-score of \(-2.0\) in August 2010 and \(-1.9\) in December 2015) and _GPP_ (approximately \(-1.9\) in October 2010), and positive anomalies for _LST_ in 2010 and 2015-2016. Considering anomalies in the hydrological variables, the 2010 drought reached more negative z-score values in April 2010 for \(P\) (\(-1.3\)), May 2010 for _SM_ and _SSM_ (about \(-2.1\) for both variables), and October 2010 for _TWSA_ (\(-1.8\)). Until October 2010, there remained very negative anomalous values for _SM_, _SSM_, and _ET_. For the 2015 drought, the most negative values were found for December 2015 for \(P\), _SM_, and _SSM_ (\(-2.0\), \(-2.2\), and \(-2.3\), respectively) and in July 2016 for _TWSA_ (\(-1.7\)).  
Drought propagation in the Cerrado was clear for the 2014 event, as demonstrated by anomalous decreases in various hydrological variables. In January 2014, the z-score for \(P\) was \(-1.4\), and the values for _SM_, _SSM_, _ET_, _EVI_, and _LST_ in February 2014 were \(-1.8\), \(-1.9\), \(-2.0\), \(-1.9\), and \(+1.9\), respectfully. The negative anomalies stood out for _TWSA_, with z-score values \(<\)\(-1\) between May 2014 and August 2015. The long drought duration in the Cerrado (with recovery in 2016) also affected _ET_, _EVI_, and _GPP_. In the Pampa biome, the hydrological variables reached negative anomalous values in January 2012, with values of \(-1.6\), \(-1.9\)\(-1.8\), \(-2.1\), and \(-1.4\) for \(P\), _SM_, _SSM_, _ET_, and _TWSA_, respectively, reaching \(-1.9\) for _TWSA_ in August 2012. The hydrological variables point to a short-duration drought that lasted less than a year and occurred during the austral summer season. A great increase in positive _LST_ anomaly values was observed in May 2012 (approximately 1.7). At the same time, the results indicated the fast evolution of _EVI_ and _GPP_ to negative anomaly values (in February 2012, the _EVI_ anomaly reached a value of \(-2.2\)).  
Table 3 summarizes the characteristics of the drought events according to onset, duration, and maximum intensity. This enabled the visualization of drought propagation characteristics on climatic and hydrological variables and vegetation indices, especially considering the duration and severity (maximum intensity). The difference between the 2010 and 2015 droughts in the Amazon became clearer, highlighting \(P\), _ET_, and _TWSA_. The _SM_ and _SSM_ in 2015 showed more months with negative anomalies, although their severity was variable and did not always reach the threshold of \(-1\). In addition, the duration of the Cerrado 2014 drought is noteworthy, especially for _ET_, _TWSA_, and _GPP_. In the Pampa biome, droughts usually occur in the summer (such as the 2012 drought), when there are naturally higher temperatures. The event started with a reduction in \(P\) and all other variables already registered negative anomalies in the following month, with the effect of propagation being more present when the duration of these anomalies was evaluated (see _SM_, _SSM_, and _TWSA_).  
Figure 4: Temporal drought patterns (2010 to 2020) for analyzed variables in the three Brazilian study areas: (**a**) the Amazon, (**b**) Cerrado and (**c**) Pampa; being (**a1**), (**b1**), and (**c1**) for \(P\), \(SM\), \(SSM\), \(ET\), and \(TWSA\); (**a2**), (**b2**), (**c2**) for \(EVI\) and \(GPP\); and (**a3**), (**b3**), and (**c3**) for \(LST\). The hatched area represents z-score \(\leq-0.5\) verified in dry periods with long effect in the analyzed variables (approximately 2010 and 2015 for the Amazon, 2014 for the Cerrado, and 2012 for the Pampa).