The 2019 WTA Clay Court season gets underway this week at the Volvo Car Open, which means it's time to revisit the WTA Insider Clay Court Power Rankings to highlight the players primed to surge ahead on the terre battue.

The WTA Insider Clay Court Power Index is based on an empirical formula that isolates a player's success rate on clay courts. To measure a player's recent aptitude on the surface, the Insider team applied the following formula, which takes into account a player's results over the last four seasons:

100% of points earned on clay courts in 2019
75% of points earned on clay courts in 2018
50% of points earned on clay courts in 2017
25% of points earned on clay courts in 2016

The resulting sum accounts for a player's "Clay Court Index."

Note that the Power Index formula has been adjusted in 2019. In previous years, 100% of the points earned from the current season and previous season were taken into account. In order to provide a more accurate reflection of recent form, the revised formula takes 100% of the points from the current season and 75% of the previous season.

As a refresher, here's who dominated the clay swing in 2018:

Roland Garros: Simona Halep d. Sloane Stephens
Madrid: Petra Kvitova d. Kiki Bertens
Rome: Elina Svitolina d. Simona Halep
Stuttgart: Karolina Pliskova d. CoCo Vandeweghe
Charleston: Kiki Bertens d. Julia Goerges

Prague: Petra Kvitova d. Mihaela Buzarnescu
Lugano: Elise Mertens d. Aryna Sabalenka
Rabat: Elise Mertens d. Ajla Tomljanovic
Strasbourg: Anastasia Pavlyuchenkova d. Dominika Cibulkova
Nuremberg: Johanna Larsson d. Alison Riske
Bogota: Anna Karolina Schmiedlova d. Lara Arruabarrena
Istanbul: Pauline Parmentier d. Polona Hercog

Here are the Top 20 on the WTA Insider Clay Court Power Rankings as the 2019 clay season begins this week in Charleston. 

No.1 Simona Halep (WTA Rank: No.2)
Career Clay Court Win %:
72.2%
2018 Clay Court Record: 16-3 (84.2%)
Notable recent clay court results: Reigning Roland Garros champion, 2018 Rome finalist, 2018 Madrid semifinalist, 2017 Roland Garros finalist, 2017 and 2016 Madrid champion, 2017 Rome finalist, 2016 Roland Garros Round of 16.

No.2 Kiki Bertens (WTA Rank: No.6)
Career Clay Court Win %:
69.3%
2018 Clay Court Record: 15-5 (75.0%)
Notable recent clay court results: 2018 Madrid finalist, 2018 Charleston champion, 2017 Gstaad champion, 2017 and 2016 Nuremberg champion, 2016 Gstaad finalist.

No.3 Elina Svitolina (WTA Rank: No.8)
Career Clay Court Win %:
64.6%
2018 Clay Court Record: 9-3 (75.0%)
Notable recent clay court results: 2018 and 2017 Rome champion, 2017 Roland Garros quarterfinalist, 2017 Istanbul champion, 2016 Roland Garros Round of 16.

No.4 Garbiñe Muguruza (WTA Rank: No.19)
Career Clay Court Win %: 64.9%
2018 Clay Court Record: 7-4 (63.6%)
Notable recent clay court results: 2018 Roland Garros semifinalist, 2016 Roland Garros champion, 2017 and 2016 Rome semifinalist, 2017 Roland Garros Round of 16. 

No.5 Jelena Ostapenko (WTA Rank: No.31)
Career Clay Court Win %:
63.6%
2018 Clay Court Record: 3-4 (42.9%)
Notable recent clay court results: 2017 Roland Garros champion, 2018 and 2017 Rome quarterfinals, 2018 Stuttgart quarterfinals, 2017 Charleston finalist, 2017 Prague semifinalist. 

No.6. Karolina Pliskova (WTA Rank: No.4)
Career Clay Court Win %:
57.7%
2018 Clay Court Record: 12-4 (75.0%)
Notable recent clay court results: 2018 Stuttgart champion, 2018 Madrid semifinalist, 2017 Roland Garros semifinalist, 2017 Rome quarterfinalist, 2017 Stuttgart quarterfinalist, 2016 Prague semifinalist, 2016 Stuttgart quarterfinalist.

No.7 Sloane Stephens (WTA Rank: No.8)
Career Clay Court Win %:
59.3%
2018 Clay Court Record: 12-5 (70.6%)
Notable recent clay court results: 2018 Roland Garros finalist, 2016 Charleston Champion.

No.8 Caroline Garcia (WTA Rank: No.20)
Career Clay Court Win %:
58.8%
2018 Clay Court Record: 13-5 (72.2%)
Notable recent clay court results: 2018 Roland Garros Round of 16, 2018 Rome quarterfinalist, 2018 Madrid semifinalist, 2018 Stuttgart semifinalist, 2017 Roland Garros quarterfinalist, 2016 Strasbourg champion.

No.9 Petra Kvitova (WTA Rank: No.3)
Career Clay Court Win %: 66.4%
2018 Clay Court Record: 15-3 (83.3%)
Notable recent clay court results: 2018 Madrid champion, 2018 Prague champion, 2016 Stuttgart semifinalist.

No.10 Madison Keys (WTA Rank: No.18)
Career Clay Court Win %:
62.3%
2018 Clay Court Record: 11-4 (73.3%)
Notable recent clay court results: 2018 Roland Garros semifinalist, 2018 Charleston semifinalist, 2016 Roland Garros Round of 16, 2016 Rome finalist. 

Here's who rounds out the Top 20:

No.11 Anastasija Sevastova (WR No.12): 1064.3
No.12 Daria Kasatkina (WR No.22): 1053.8
No.13 Samantha Stosur (WR No.73): 1027.5
No.14 Anett Kontaveit (WR No.14): 989.8
No.15 Maria Sharapova (WR No.28): 902.0
No.16 Elise Mertens (WR No.17): 900.0
No.17 Kristina Mladenovic (WR No.66): 863.3
No.18 Caroline Wozniacki (WR No.13): 860.5
No.19 Irina-Camelia Begu (WR No.69): 854.5
No.20 Laura Siegemund (WR No.104): 842.8