Investigating Brazil's Chance of Heavy Rainfall After Heatwaves:National Weather Center Presentation

rainb events in Brazil so first off I'd like to thank my mentor Dr Elanor Martin for supporting me in this project as this project wouldn't be possible without her help so I'm going to be investigating the probability of compounding Heatwave and extreme rainfall events in Brazil so heat waves as you probably know typically bring extreme impacts across the globe in fact one of the leading causes of weather related deaths throughout the world is through um is due to heat waves however an indirect impact that isn't commonly associated with heat waves is a possibility of extreme rainfall um happening shortly after Heatwave termination as this has been a common occurrence in numerous areas of the world as you could probably see in places like Europe Japan as well as the northeastern portion of the United States those areas simply um have a much higher probability of experiencing extreme rainfall after a heat wave ends where it um the percentage hovers right around a 30% chance of extreme rainfall happening which is much higher um compared to their da average when it um when it comes to extreme rainfall um however this um event hasn't been thoroughly investigated in Brazil and how it could pose a significant threat to the country as Brazil's urb Urban environment and infrastructure where the majority of the population lives is very vulnerable to extreme rain um weather events such as flooding um since a lot of these cities in Brazil were built over flood planes so that makes some um a large portion of the population extremely vulnerable to extreme rainfall events and flooding and 74% of deaths U um related to natural disasters in Brazil have been attributed to extreme rainfall events inducing flooding and mudslides so it's very important that we really identify any sort of trend when it comes to the possibility of extreme rainfall happening shortly after heat waves and due to climate change the frequency of heat waves in Brazil have been increasing which raises a concern that along with heat waves we could see more extreme rainfall events um increase in Brazil as time goes on and as you um as you could see with the graphs for um so Paulo on Brazil we see that the trend for heat waves have been increasing over the past um several decades especially in the past three decades and then for mon Brazil we also see that Trend occur where the frequency of heat waves have been increasing by U um by a lot over the past few decades um therefore the objective of this project is to investigate the probability of extreme rainfall events happening shortly after a heat wve terminates um to better predict the long-term more localized effects of climate change in Brazil and how it could um affect a country directly based on how vulnerable each um city is so um the way I'll be doing this is by taking a look at the daily maximum temperatures um for Brazil um between 1961 and 2020 as the data I will be pulling from it um comes from over a thousand different weather stations throughout the country I'll also be using daily precipitation data between 1961 and 2020 and in terms of the criteria I'll be using when it comes to um defining what a heatwave is there isn't really a set definition but the criteria that many studies use is typically using the 90th percentile threshold where um the where the temperature needs to be above the 90th percentile for at least three consecutive days for it to be considered a heat wave and then when it comes to extreme rainfall um event would be considered an extreme rainfall if the da precipitation exceeds the 95th percentile and for it to be associated with the heat waves it would need to happen within 48 hours after the last day of the heat wave so some of the method um so um the places I'll um I'll take a look at five different cities in Brazil that which Encompass um five different regions because of course every region in Brazil is very different when it comes to the climate so a city that might experience a compounding extreme rainfall right after a heat wave might not necessarily see that in another city where the climate is very different so we're going to be taking a look at that at five different regions and python code will be used to extract um the events that meet the Heatwave and extreme rainfall criteria and here's an example of this so this is a temperature and precipitation data for so Paulo Brazil where the um graphs would detect where the heat waves are detected where the temperature is above the 90th percentile and where the extreme rainfall is above the 95th percentile and as you could see there were several instances where heat waves were detected during the year um 2011 there wasn't really any compounding effects um in um this specific year but in many other instances for a so po we did see uh we did see evidence of extreme rainfall um um happening shortly after Heat Wave occurs so in terms of the results for so pow Brazil so the average annual number of heat Waves per year is hovering around 4.6 of five heat waves um per year and of course that has been increasing over the past um several decades and then the daily climatological average of um extreme rainfall H occurring in any given day is around 4% but uh the probability of that happening after a heatwave raises all the way up to 23% % chance so there's nearly a six time um you're nearly six times more likely to experience an extreme rainfall event um um right after a heat wave compared to average for so um Paulo Brazil which really gives a good indication that um heavy rainfall does um is very prevalent in Brazil right after a heatwave and for another city in manow Brazil which is a little bit further northward and a little bit further um Westward with the average annual amount of heat waves is very similar to what we saw in so Paulo Brazil which is around 4.5 um however we didn't see really any sort of probability increase um after a heat um after Heatwave termination um compared to the climatological average where it pretty much remained at 5% um whether it was right after a heat wave or um just um compared to the average so there doesn't seem to be a trend when it comes to extreme rainfall happening after a heatwave so Northern Brazil receives mostly stable temperatures throughout the year as you could clearly see it's um um while Southern Brazil um varies sign more significantly when it comes to temperture um throughout the um different seasons and the th and um as you probably noticed with the mean annual heat waves most of the heat waves tend to occur right around the Southeastern portion of the country where the temperature is a bit more variable between Seasons which could indicate that the the areas that have a little bit more variation when it comes to temperature between seasons are um do um have a higher possibility of experiencing the compounding Heatwave and extreme rainfall events and due the fact that these areas experience more heat waves we um there could be that possibility that the southern portion of the country would also experience more extreme rainfall events shortly after a heat wave terminates and um especially as heat waves continue to increase over the next several years so in um for the summary um so so um so paollo Brazil is 5.75 times more likely compared to average to receive an extreme rainfall event after a heat wave terminates and then extreme rainfall events are likely to increase for so pal um Paulo as heat wave frequency increases and then Heatwave terminations also have no noticeable impact in terms of probability of extreme rainfall in monis um Brazil as it seems like in the areas a little bit fur northward with less temperature variation there's less likely of a shot you're going to experience um the phenomenon where you're going to where extreme rainfall would occur after Heatwave terminations and then temperate regions of Brazil are significantly more likely to receive um heat waves compounding extreme um rainfall events so it's defly important for um the areas um in southern Brazil to pay attention to that trend where the possibility of extreme rainfall is far more likely in that area of the country and that's it any questions days so um so your question was if there's extreme rainfall right after he waves and what's my definition for it so um so my definition for it was um would be that the extreme rainfall event would need to happen at least 48 hours after a heat wave ends after the final day of the heat wave which is my criteria for determining if extreme rainfall was associated with um the heat wave was wondering much so um when it comes to the frequency of heat waves I'm rising due to the observational Network so um in this instance I use um um so pal and Maus as my main cities I was focusing on I'mma also um I'mma also take a look at other cities as well so in those cities it's um there were um quite a bit of um observational um areas where they could receive data from um it's only more so in the Northwestern portion of Brazil closer to the Amazon forest that's where it it um the data does become definitely more sparse but in the cities um I showed it's um it doesn't seem like there was um that the increased amount of um observational um areas um really um contributed much to the increasing heat waves as it's pretty much just been on natural from what I've seen question I have a question um but one of you like one of your first figures was you showing like a heat wve and then how some of them had the extreme rainfall afterwards I was wondering if you looked into why like what kind of maybe like synoptic conditions were in place when there was that extreme precipitation event afterwards and when there wasn't so I haven't taken a look at that specifically but um due to fact that um many of these extreme rainfall events compounding heat waves occur more more in the temperate regions of Brazil where there's a bit more um temperature variability I assume it would be more associated with um with um instability um that's associated with cold fronts let's say um because of course during a heatwave um the humidity begins to rise up until the final day of the Heat Wave and once the heat wave ends there needs to be at least some sort of cold pocket and that cold pocket likely enhances um thunderstorm development in the southern portion of the country thank you any other questions okay thank you for a great talk